Have a customers machine here that keeps getting the same errors repeatedly, I have formatted and installed XP pro 3 times now. The error is file corruption:

'Windows could not start because the following file is missing or corrupt:
\WINDOWS\SYSTEM32\CONFIG\SYSTEM'

It works fine for a week or so after re-format then get the above error. Heres what I have tested:

Overnight diagnostic with MS Windows Memory Diagnostic (mtinst.exe) - No errors, I suspected RAM at first.

Heat: runs at around 55, with 3 case fans.

It runs fine after the install at my place and then again for around a week at the customers before the black screen pops back again. I'm now suspecting power supply so will test with a different one after the fourth re-install. Any thoughts?