Any thoughts on what is gone wrong with my laptop.
Symptoms. Screen is covered in coloured blocks which come and go if the case is twisted a few millimeters. It is dead slow and is making desisions on its own.

Howdy 3006. I have a laptop that exhibits similar problems. It was dropped on one corner near the LCD screen. Even snapped the Hinge. I have fixed it (the broken hinge part of it) using a Drill, tap and die, some jb weld, a 8-32 screw and a fender washer. However sometimes I need to tap the side of the screen to get a unscrambled display. I blame it either on the ribbon cable for the LCD, or the video card, or some other loose connection from it being dropped. It is not worth it to me to totally repair it completely as the laptop is a PII 256 mb of ram. It works ok for what I did to it.

If your laptop was ever dropped for any reason this could be a cause. Another thing I would try is to pull the battery, and run it just on the ac adapter and see if same problems persist. Just a easy way to troubleshoot is all I am suggesting. Good Luck.

Have you tried uninstalling and reinstalling the drivers?