Get an Ubuntu / Knoppix / Puppy / Slax disk, run memtest86 - easiest from an Ubuntu disk, just run memory test.
The black + reboot behavior means you haven't changed the default blue screen settings and it wants to show you a blue screen.
Sounds like a RAM, OS or PSU problem - if Ubuntu runs fine from it's LiveCD, it's probably a corrupted XP install.
You can save the files from your hard drive to an external FAT32 drive with any of those, and with Ubuntu and the Knoppix DVD to a NTFS-formatted external drive too. The ntfs-3g in latest Knoppix CD is a bit old and has trouble mounting NTFS drives in read/write mode. If you didn't understand the previous sentence, you want the latest Knoppix DVD or Ubuntu / Kubuntu 8.10 LiveCD.
If the memory is at fault, memtest86 will report it easy enough. If it's the PSU, Linux will likely reboot randomly too.
The black + reboot behavior means you haven't changed the default blue screen settings and it wants to show you a blue screen.
Sounds like a RAM, OS or PSU problem - if Ubuntu runs fine from it's LiveCD, it's probably a corrupted XP install.
You can save the files from your hard drive to an external FAT32 drive with any of those, and with Ubuntu and the Knoppix DVD to a NTFS-formatted external drive too. The ntfs-3g in latest Knoppix CD is a bit old and has trouble mounting NTFS drives in read/write mode. If you didn't understand the previous sentence, you want the latest Knoppix DVD or Ubuntu / Kubuntu 8.10 LiveCD.
If the memory is at fault, memtest86 will report it easy enough. If it's the PSU, Linux will likely reboot randomly too.