Have you tried switching your PC off and trying again? I know it seems obvious, but occasionally, I get a strange boot-up, and this clears it.
Next, try un-plugging your graphics card cable and re-connecting. It's amazing what a minor connection problem will cause, if that doesn't work, try gently wiggling the cable at each end during boot-up, and see if the situation improves. Broken or loose wires are often found at the extremities of the cable.
Further, (taking anti-static precautions), remove your graphics card from the machine and try GENTLY cleaning the connectors. Be careful not to touch them with your hands. Apart from the static risk, grease can be removed from you to the connectors, and eventually cause corrosion.
Finally, your down to substitution. Have you got an old graphics card you can use to try, or maybe borrow a friends monitor to see if you still have the problem?