After C Drive upgrade, Retrospect 7.5 will not back up from C

[RMJohnson]

My main drive was getting full so I purchased a Seagate PATA drive and ran their drive wizard to clone my old drive over to the new one. It worked perfectly...except that Retrospect crashes when it starts to back up any file from my new C drive. It backs up clients on other computers, it backs up my D and E drives fine. I have erased the backup scripts for C, re built, samo. Uninstalled Retrospect 7.5 and rinstalled, samo. Did multiple drive tests with Seagate Seatools, all ok, used Windows drive tests, samo. If I set up a backup of even 1 file from C drive to external USB or to an internal hard drive, as soon as it actually starts the execution access to the drive, system reboots. Running AMD 3000+, XP Home SP2. Everything else is good! Any ideas? Thanks