SLI problems

[paliopetho]

After swapping my 20" Syncmaster for a 32" LCD TV, I can not get SLI to run properly. In the Nvidia control panel, when I try to enable SLI, the screen goes black, the computer resarts and brings me to the safe mode normal mode prompt. I go to normal mode, the screen flickers and games won't run properly. The game Trackmania flickers unbareably, worse than the desktop. Tomb Raider Anniversary won't even load, screen goes black, computer restarts and goes to safe mode, normal mode prompt. Disabling SLI makes all games runs great. Should I replace the two 7950 gt's with one 8800? Because even one 7950 gt looks great.

Windows Vista Home Premium,
Dual Nvidia 7950 gt 512MB, (drivers are up to date)
750W PSU
2GB ram
200GB HDD
AMD Athlon 64 X2 5200+ Dual-Core
Asus M2N32-SLI Deluxe.