Hi Moira,
I am sorry I forgot to mention that the Dimension 9100 shipped with DDR2 PC4200 memory. Eileen has a Dimension 8100 which uses Rambus RDRAM PC800................. even more exotic!
I think that what must have happened is your Dad will have overwritten the hidden recovery partition when he formatted. The recovery disk is little more than a boot disk that lets you access the recovery partition, so it won't find anything now.
I also suspect that the MBR has been corrupted, which could be why the XP installation cannot find the disk properly.
Overwriting the whole disk should present it with what appears to be a brand new HDD. Normally I would use the HDD manufacturer's diagnostic tool for this, as I think that there is a better chance of error detection and remediation.
However, DBAN should wipe the drive and I would expect it to display messages if there are physical problems with the disk.
One thing to check:
Go into "Set Up" (should be F2) and look for an entry like:
Primary Drive 0...............................................Hard Drive
Open that and make sure that it is set to "Auto"
Scroll down and find the entry:
PC Speaker.........................................On
That should get you any BIOS beep codes.
Then:
Fast Boot............................................Off
You will have a better chance of catching BIOS error messages that way ;)
