|Boot into Safe Mode, if all looks good there, you have a corrupted video driver, download a new driver for your video card or motherboard if you are using onboard video.|
If you still get this in Safe Mode then try borrowing a monitor and cable and try all combinations to see if you can definitely confirm or eliminate whether it is the video card./onboard video or your monitor or cable is definitely bad. If your video is bad, purchase a video card, if you prove that it is the cable, return the cable you purchased and get a better one, if you prove it is the monitor, then replace that.
Just keep in mind that you have an older system and you should avoid spending too much on it since you will be replacing it eventually, probably within a year or maybe two. A decent monitor may be worth spending a little but more on since you could use it on your next system so keep that in mind as well.
You have to be a little bit crazy to keep you from going insane.