The monitor cable has 3 main shielded wires and many other ones. Those wires can break contact with bending or constant bend, especially jammed against the wall.
Or the video connector pins have corroded a little. Or the holes those pins go into have widened out.
Jiggling the cable doesn't affect the card.
Your error messages are another story...post actual messages. Viruses, spies, malware usually are the cause. Clean up!
I have an HP Pavilion 7865 running Windows ME. My montor is a Pavilion mx70. The problem is with the monitor. Horozontal lines appear on the screen that seem to be randomly placed, they also scroll with the text of the screen (When i move the text up and down). It also sometimes gets very dim. The real trick is that when i check in the back of the computer and jiggle the monitor cable, the screen will flicker with the jiggling and return ot normal. I also have problems with error messages, mostly with programs doing illegal oporations. This sometimes leads to the blue screen of death. My real quesiton is, I know that it is the video card, what i am trying to ask, could a bad video card cause your computer to crash and have error messages constantly? THANKS!