Im having troubles with a system. After installing graphics drivers, I checked device manager and it shows that one out of the 4 gtx680's is not working. Says something about could not start due to not having enough resources. The M/B is Gigabyte x79-up4 which supports 4 way SLI, so having 4 gtx 680's shouldn't be a problem. I don't think any of the graphics card is dead either, as they work fine one by one.