Hey, a little over a month ago, I built my new computer. ASUS P5RD1-VM motherboard, Intel Pentium 4 processor, 80GB HDD, a CD-ROM RW drive, and a DVD-ROM drive. Power supply is a 24pin 12V, RAM is 512 MB DIMM by Elixir, and the video card is a Radian 1500.
A few weeks ago, the PSU died, and the motherboard fried. I had both replaced, and picked it up a few days ago. Now the computer boots up, and enters Windows XP but, after I log on, and am at the desktop, the computer shuts off. I've tried reseating the RAM, and switching power cords, but it doesn's seem to help any, as the computer still shuts off every time I enter the desktop. Why is it doing this?
Thanks in advance for any help.

If your MB fried and PSU Died it is possible that you have not setup your bios correctly, make sure that you have FSB and memory timings set correctly and that any jumpers on MB for setting FSB are correctly set. have you reinstalled windows? and is your HDD configured corectly?