What am i not doing correctly to get my 2 video cards working SLI with the onboard monitor output?

brief description of system

motherboard-----asus m3n-ht deluxe series

cpu----AMD phenom quad core x 2 9950 black edition

pci express----2 X nvidia g-force 8800 GTX 768mb DDR3 video cards

power supply 850 watts

os ---windows vista ultimate edition 64 bit

bios is updated and everything was working good then i had a power surge or / outage and then i got little yellow group patterns in diffrent spots on the monitor screen and some screens its there and some its not . ive tryed to re install the video drivers but nothing changed, so i shut it down and pulled the cards and when i tryed to re install them back on the mother board i got no video at all. the monitor stays blank and nothing else happens at all. but when they are out i get a picture off the onboard output but none with the cards in . not even the card outputs. its like my computer just hangs . how can i install the cards and get video from the motherboard output so i can run the cards in SLI mode .is there somthing in the system bios i didnt do . and ive reset bios also and if the cards are in. nothing. when theyre out i get picture. this is driving me to kill bill gates help please!!!!!!!!!!!!!!|||Try one card at a time - one of them could have gotten fried during the surge. If your extremely unlucky, both of them could have gotten fried. If that is the case, look into the warranties on them. Companies like EVGA have fantastic replacement programs.