XP machine is boot-looping; even when I try to load Knoppix.

I've been running a small box as a file server for a few years now. It's a MiniITX mobo with 2 HDDs attached. Also my print server. Stays up 24/7. Recently it started boot-looping. I haven't installed anything on it other than updates from MS.

I figured the C drive had gone bad and pulled it and replaced with a new hard drive with a fresh install of XP. Still boot-looping.

The strange thing is the it begins the loop at the exact same place as it did before I swapped drives... right as the colorful XP logo starts to fade in.

As I start trying to eliminate things, I don't feel like it's the PSU because I can leave it running on the OS recovery screen (where you pick Last Known Good, Safe Mode, etc.) for hours and it won't fail.

Other important detail is that I can't load Linux from an old Knoppix Live CD I have. It loops as well. Same when I try to load Ultimate Boot CD.

I feel like I've ruled out the HDD and PSU. That leaves RAM and Mobo right? Would bad RAM cause boot-looping?

What else? Any thoughts or suggestions?