You may follow something like this (if the problem its fixed, not continue the list):
0) Its everything well connected? all PCI cards firmly stuck?
1) try different monitor
2) try different video card
3) try with only 1 memory slot use
4) try withouth HD, floppy, CD, DVD
5) Your CPU or your motherboard its damage
6) try with other CPU
7) Your motherboard its damage

replace motherboard
9) mount everything
10) play