I'm at a WinXP SP2.It has been automatically updated recently.
The machine reboots for no apparent reason and also freezes.When one turns it on for the first time, it fails to boot for several times. Sometimes the BIOS configuration changes the boot device priorities and the systems date/time automagically. I receive the message to try f2 to reconfigure the system or it will load default value, then it freezes. Sometimes the characters are scrambled, sometimes it just freezes at the countdown to load default. It also displays a message which I can't truly read because there are many characters missing, but I'm quite sure it says something about a missing file on some Windows Folder and that I should place the Windows Installer cd in the driver. Then it iniatializes normally.
For some reason system volume information is not accessible.
Unhackme used to find a driver named machndrj.sys, but whenever I rebooted to complete the healing process it said that the file didn't exist. He finds it no more. Msconfig denies me the changes I try to make even though the user has administrator's privileges.AVG system area check finds nothing, not even when aimed at the system volume information folder.Complete detailed test always stops and sometimes reboot the system;until then,finds nothing.NOD32 says that the path to system volume information is invalid;right-click > properties says that the folder is empty.AVG finds some password protected files but no threats.

Nod32 says:
c:\pagefile.sys is blocked.At some point in the scan, the computer reboots.

This is the Hijackthis log file:

Logfile of HijackThis v1.99.1
Scan saved at 20:35:11, on 13/12/2007
Platform: Windows XP SP2 (WinNT 5.01.2600)
MSIE: Internet Explorer v6.00 SP2 (6.00.2900.2180)

Running processes:
C:\Arquivos de programas\GbPlugin\GbpSv.exe
C:\Arquivos de programas\Eset\nod32krn.exe
C:\Arquivos de programas\Java\jre1.6.0_03\bin\jusched.exe
C:\Arquivos de programas\Eset\nod32kui.exe
C:\Arquivos de programas\iTunes\iTunesHelper.exe
C:\Arquivos de programas\Lexmark 7100 Series\ezprint.exe
C:\Arquivos de programas\UnHackMe\hackmon.exe
C:\Arquivos de programas\Arquivos comuns\Ahead\Lib\NMBgMonitor.exe
C:\Arquivos de programas\Arquivos comuns\Ahead\Lib\NMIndexingService.exe
C:\Arquivos de programas\Arquivos comuns\Ahead\Lib\NMIndexStoreSvr.exe
C:\Arquivos de programas\iPod\bin\iPodService.exe
C:\Program Files\HijackThis\HijackThis.exe

R1 - HKCU\Software\Microsoft\Internet Explorer\Main,Search Bar = http://g.msn.com.br/0SEPTBR/SAOS01?FORM=TOOLBR
R1 - HKCU\Software\Microsoft\Internet Explorer\Main,Search Page = http://g.msn.com.br/0SEPTBR/SAOS01?FORM=TOOLBR
R1 - HKCU\Software\Microsoft\Internet Explorer\SearchURL,(Default) = http://g.msn.com.br/0SEPTBR/SAOS01?FORM=TOOLBR
R1 - HKCU\Software\Microsoft\Internet Connection Wizard,ShellNext = http://g.msn.com.br/8SEPTBR030000TBR...BSiteFinalMSGR
O2 - BHO: SSVHelper Class - {761497BB-D6F0-462C-B6EB-D4DAF1D92D43} - C:\Arquivos de programas\Java\jre1.6.0_03\bin\ssv.dll
O2 - BHO: (no name) - {7E853D72-626A-48EC-A868-BA8D5E23E045} - (no file)
O2 - BHO: Windows Live Sign-in Helper - {9030D464-4C02-4ABF-8ECC-5164760863C6} - C:\Arquivos de programas\Arquivos comuns\Microsoft Shared\Windows Live\WindowsLiveLogin.dll
O2 - BHO: Windows Live Toolbar Helper - {BDBD1DAD-C946-4A17-ADC1-64B5B4FF55D0} - C:\Arquivos de programas\Windows Live Toolbar\msntb.dll
O2 - BHO: G-Buster Browser Defense ABN AMRO - {C41A1C0E-EA6C-11D4-B1B8-444553540007} - C:\ARQUIV~1\GbPlugin\gbiehabn.dll
O2 - BHO: G-Buster Browser Defense Unibanco - {C41A1C0E-EA6C-11D4-B1B8-444553540008} - C:\Arquivos de programas\GbPlugin\gbiehuni.dll
O3 - Toolbar: Windows Live Toolbar - {BDAD1DAD-C946-4A17-ADC1-64B5B4FF55D0} - C:\Arquivos de programas\Windows Live Toolbar\msntb.dll
O4 - HKLM\..\Run: [SunJavaUpdateSched] "C:\Arquivos de programas\Java\jre1.6.0_03\bin\jusched.exe"
O4 - HKLM\..\Run: [SoundMan] SOUNDMAN.EXE
O4 - HKLM\..\Run: [QuickTime Task] "C:\Arquivos de programas\QuickTime\QTTask.exe" -atboottime
O4 - HKLM\..\Run: [nod32kui] "C:\Arquivos de programas\Eset\nod32kui.exe" /WAITSERVICE
O4 - HKLM\..\Run: [NeroFilterCheck] C:\Arquivos de programas\Arquivos comuns\Ahead\Lib\NeroCheck.exe
O4 - HKLM\..\Run: [lxbxmon.exe] "C:\Arquivos de programas\Lexmark 7100 Series\lxbxmon.exe"
O4 - HKLM\..\Run: [Logitech Hardware Abstraction Layer] KHALMNPR.EXE
O4 - HKLM\..\Run: [iTunesHelper] "C:\Arquivos de programas\iTunes\iTunesHelper.exe"
O4 - HKLM\..\Run: [FaxCenterServer4_in_1] "C:\Arquivos de programas\Lexmark 7100 Series\fm3032.exe" /s
O4 - HKLM\..\Run: [EzPrint] "C:\Arquivos de programas\Lexmark 7100 Series\ezprint.exe"
O4 - HKLM\..\Run: [AVG7_CC] C:\ARQUIV~1\Grisoft\AVG7\avgcc.exe /STARTUP
O4 - HKLM\..\Run: [LXBXCATS] rundll32 C:\WINDOWS\System32\spool\DRIVERS\W32X86\3\LXBXtime.dll,_RunDLLEntry@16
O4 - HKCU\..\Run: [UnHackMe Monitor] C:\Arquivos de programas\UnHackMe\hackmon.exe
O4 - HKCU\..\Run: [CTFMON.EXE] C:\WINDOWS\system32\ctfmon.exe
O4 - HKCU\..\Run: [BgMonitor_{79662E04-7C6C-4d9f-84C7-88D8A56B10AA}] "C:\Arquivos de programas\Arquivos comuns\Ahead\Lib\NMBgMonitor.exe"
O4 - Global Startup: Adobe Gamma Loader.lnk = C:\Arquivos de programas\Arquivos comuns\Adobe\Calibration\Adobe Gamma Loader.exe
O8 - Extra context menu item: &Windows Live Search - res://C:\Arquivos de programas\Windows Live Toolbar\msntb.dll/search.htm
O8 - Extra context menu item: Abrir em uma nova guia do plano de fundo - res://C:\Arquivos de programas\Windows Live Toolbar\Components\pt-br\msntabres.dll.mui/229?1608e3ac1dd445ea945ee3b9c1130fec
O8 - Extra context menu item: Abrir em uma nova guia do primeiro plano - res://C:\Arquivos de programas\Windows Live Toolbar\Components\pt-br\msntabres.dll.mui/230?1608e3ac1dd445ea945ee3b9c1130fec
O8 - Extra context menu item: Add to Windows &Live Favorites - http://favorites.live.com/quickadd.aspx
O8 - Extra context menu item: E&xportar para o Microsoft Excel - res://C:\ARQUIV~1\MICROS~1\OFFICE11\EXCEL.EXE/3000
O9 - Extra button: (no name) - {08B0E5C0-4FCB-11CF-AAA5-00401C608501} - C:\Arquivos de programas\Java\jre1.6.0_03\bin\ssv.dll
O9 - Extra 'Tools' menuitem: Sun Java Console - {08B0E5C0-4FCB-11CF-AAA5-00401C608501} - C:\Arquivos de programas\Java\jre1.6.0_03\bin\ssv.dll
O9 - Extra button: Pesquisar - {92780B25-18CC-41C8-B9BE-3C9C571A8263} - C:\ARQUIV~1\MICROS~1\OFFICE11\REFIEBAR.DLL
O10 - Unknown file in Winsock LSP: c:\windows\system32\avgfwafu.dll
O10 - Unknown file in Winsock LSP: c:\windows\system32\avgfwafu.dll
O10 - Unknown file in Winsock LSP: c:\windows\system32\avgfwafu.dll
O10 - Unknown file in Winsock LSP: c:\windows\system32\avgfwafu.dll
O10 - Unknown file in Winsock LSP: c:\windows\system32\avgfwafu.dll
O14 - IERESET.INF: SEARCH_PAGE_URL=&http://home.microsoft.com/intl/br/access/allinone.asp
O16 - DPF: {2BC66F54-93A8-11D3-BEB6-00105AA9B6AE} (Symantec AntiVirus scanner) - http://security.symantec.com/sscv6/S...in/AvSniff.cab
O16 - DPF: {644E432F-49D3-41A1-8DD5-E099162EEEC5} (Symantec RuFSI Utility Class) - http://security.symantec.com/sscv6/S.../bin/cabsa.cab
O16 - DPF: {E37CB5F0-51F5-4395-A808-5FA49E399007} (GbPluginObj Class) - https://wwws.realsecureweb.com.br/mp...bPluginABN.cab
O16 - DPF: {E37CB5F0-51F5-4395-A808-5FA49E399008} (GbPluginObj Class) - https://clickbanking.unibanco.com.br...bPluginUni.cab
O17 - HKLM\System\CCS\Services\Tcpip\..\{964F8589-F38F-448B-8622-241D7BA636F0}: NameServer =
O18 - Protocol: livecall - {828030A1-22C1-4009-854F-8E305202313F} - C:\ARQUIV~1\MSNMES~1\MSGRAP~1.DLL
O18 - Protocol: msnim - {828030A1-22C1-4009-854F-8E305202313F} - C:\ARQUIV~1\MSNMES~1\MSGRAP~1.DLL
O20 - Winlogon Notify: GbPluginAbn - C:\ARQUIV~1\GbPlugin\gbiehabn.dll
O20 - Winlogon Notify: avgwlntf - C:\WINDOWS\SYSTEM32\avgwlntf.dll
O20 - Winlogon Notify: __GbPluginAbn - C:\Arquivos de programas\GbPlugin\gbiehabn.dll
O21 - SSODL: WPDShServiceObj - {AAA288BA-9A4C-45B0-95D7-94D524869DB5} - C:\WINDOWS\system32\WPDShServiceObj.dll
O23 - Service: AVG7 Alert Manager Server (Avg7Alrt) - GRISOFT, s.r.o. - C:\ARQUIV~1\Grisoft\AVG7\avgamsvr.exe
O23 - Service: AVG7 Update Service (Avg7UpdSvc) - GRISOFT, s.r.o. - C:\ARQUIV~1\Grisoft\AVG7\avgupsvc.exe
O23 - Service: AVG7 Resident Shield Service (AvgCoreSvc) - GRISOFT, s.r.o. - C:\ARQUIV~1\Grisoft\AVG7\avgrssvc.exe
O23 - Service: AVG E-mail Scanner (AVGEMS) - GRISOFT, s.r.o. - C:\ARQUIV~1\Grisoft\AVG7\avgemc.exe
O23 - Service: AVG Firewall (AVGFwSrv) - GRISOFT, s.r.o. - C:\ARQUIV~1\Grisoft\AVG7\avgfwsrv.exe
O23 - Service: Gbp Service (GbpSv) - Unknown owner - C:\Arquivos de programas\GbPlugin\GbpSv.exe
O23 - Service: InstallDriver Table Manager (IDriverT) - Macrovision Corporation - C:\Arquivos de programas\Arquivos comuns\InstallShield\Driver\11\Intel 32\IDriverT.exe
O23 - Service: iPod Service - Apple Inc. - C:\Arquivos de programas\iPod\bin\iPodService.exe
O23 - Service: lxbx_device - Lexmark International, Inc. - C:\WINDOWS\system32\lxbxcoms.exe
O23 - Service: NBService - Nero AG - C:\Arquivos de programas\Nero\Nero 7\Nero BackItUp\NBService.exe
O23 - Service: NMIndexingService - Nero AG - C:\Arquivos de programas\Arquivos comuns\Ahead\Lib\NMIndexingService.exe
O23 - Service: NOD32 Kernel Service (NOD32krn) - Eset - C:\Arquivos de programas\Eset\nod32krn.exe
O23 - Service: PC Tools Auxiliary Service (sdAuxService) - PC Tools - C:\Arquivos de programas\Spyware Doctor\svcntaux.exe
O23 - Service: PC Tools Security Service (sdCoreService) - PC Tools - C:\Arquivos de programas\Spyware Doctor\swdsvc.exe