dead PCIe slot? mainboard? software issues?

Hello everyone before i start i just want to say i have not come here out of laziness!. i did google and i have tried everything i can think so.

Here is the problem it all started with what i thought was a bad gtx470, I sent it in for replacement. I then got my replacement Yay i thought problem solved i'll be back to slaughtering the inccocent in the mean streets of gta4 in no time. i had basicly the same problem. a runtime error .

Sometimes just at desktop my screen would go black and then come back with a message "display has stopped working but was restored" and sometimes it would just stay black and frozon. i had my psu taken to the local pc shop to have it tested. The guy found an PCIe 6+2 connector to be dead and all others he tested to be working. So i got a new psu today. by this time i was really pumped! no way this won't solve all my pc troubles i thought as i was finishing up my cable managment, game on!

Now i have basicly the same problem...more black screens with following fore mentioned messages telling me that my display had stop working which i already knew. and that the display was restored ..which i was also able to determine on my own. But now its much more stable i can actually work and chat on it as much as i like. as as before the pc was impossible to use due to these black outs and freezes. I'm still unable to play any games. i have an sli board so i thought just for fun i'll stick in the bottom slot to see what happens. It still just gives me runtime errors on the first screen of gta4 and portal 1 a game from 2006 freezes on main game menu. gpu-z shows everything working fine at desktop.
The only thing i can do now is get a new mainboard. Unless somone can help. Thanks in advance.

 

If it works fine until you tax the system by playing games, then that points to heat, RAM, or power. Assuming you replaced it with an good PSU with adequate power, I would look at heat first. Make sure the interior is clean of heat trapping dust and that you have plenty of front-to-back air flow through the case. Consider blasting a desk fan into the open side and see what happens.

Run with just one stick of RAM at a time and see what happens.

And just in case, I would swap monitors to ensure it is not your monitor that is losing sync with the card.

 

Have you tried reinstalling the nVidia driver yet and/or bringing it up to the newest, 275.33 ATM, they change so quickly. This is in conjunction with what Digerati said above, try the driver update and then do the hardware dance. Easiest first as I always say. You can also run Memtest86 to test your RAM.