As stated earlier, the trouble your experiencing is most likely being caused by a kernel mode rootkit... If it is a desperatley mission critical machine, there is one thing you could 'try' to remediate the problem. Since rootkits typically patch the system call table, to redirect or 'hook' calls, you could try to backup an un-patched/infected table. Obviously, the most reliable solution is to completely reinstall... i just thought i would input my 2 cents. Hope it helped.

- shell