Here's some trouble shooting things you can try.
If you have a CPU with integrated graphics pull out the video card, go into BIOS and enable onboard graphics and see what happens.
Answer- If everything works alright than you know either the video card or PCI-e slot is at fault.
If you have a spare video card or know someone with a spare take out the old video card and replace it with the spare and see what happens
Answer- If the problem goes away it's the original video card you were using. If the problem continues than it's probably a bad PCI-e slot