Win XP Pro - Blue screen crash on boot

The BSOD error is an IRQL NOT LESS OR EQUAL with the code of 0x0000000A. Some research told me that simply replacing the boot files (primarily the NTLDR file) will solve the problem. So I replaced the files, and the system booted to the desktop and ran perfectly until I powered off and tried to reboot. It again crashed to the same error. So I replaced the boot files again, and again it worked perfectly, but again just once. I have run full hardware diagnostics on the hard drive and RAM, and everything there is OK. Any ideas?

 

Oh yeah - when I try a Safe Mode boot, I get a totally different error on a black screen: TRAP 00000006 EXCEPTION. There's also TONS of other codes and numbers on the screen, far too many to list here. It was during the research of this error that led me to replacing the boot files.