Constant Rebooting and System Error Messages

Question

ASROCK MOTHERBOARD: BIOS ver: 1.50
MEMORY: PC2700 @ 256 X 2 (512 MB) I have 2 @ 512 PC2700 and it will make the machine stop.

I have reinstalled Windows XP Home SP-2 several times and the problem is still the same. The PSU is 450 Watts.

This machine will reboot without warning and almost constantly.

Any ideas will be helpful.

Thanks,

Bene