You just have to troubleshoot it the list is huge to test, only 1 in 100 times can one of the members just guess what is wrong with your system you have to eliminate one component at a time.
0. Is nothing shorting out, Lose screw in the case, bit of damp dust some where?
1. Test your cable connections, DVI HDMI whatever you are using
2. make sure the power connectors are plugged into your video card fine and that your video card is secure on the motherboard.
3. Go get a second screen and unplug your screen and try that.
4. Re install the drivers
5. Test the video card in another system if nothing is fixed and the video card works fine in another system now you know its not the screen or video card.
6. remove you OC settings if you have OC'd
7. If you have more than one stick of RAM remove one. if it don't wak still swap the sticks over, if still not working test the RAM in a different slot, If it still isn't working the RAM should be ok but if you want to make sure test it in another system. If it works its not the RAM.
8. Test another PSU in the RIG, a power supply supplying incorrect power to components could cause this.
9. Their maybe a issue with the OS install or the HDD, Re install windows to a second HDD to test it.
10. If all this has not fixed your issue it will either be a motherboard fault or CPU fault you can only test this if you have the same socket CPU and mobo around to test.
Fixing Computing issues - Process of elimination