Just a thought, before you replaced the video card did you first uninstall the driver for the old card? Are you running the most up to date driver for the new card? Have you tried placing in your old card to see if the issue goes away? That is what I would start with to rule out the video card or video card software as being the problem. If it is not the problem, the next would be moving to troubleshooting the powersupply. Have you double-checked all of the connections to make sure you have them all plugged in on the motherboard (some just have a single 24 pin connector, some have a 20 pin and a seperate 4 pin)?