It's a Dell running Win XP (SP3), and has an Nvidia GeForce 8300 GS graphics card. I *think* the card is broken. For the last few weeks, every time it runs, either lots of green/magenta dots appear on the screen, or it blue screens. When it blue screens, the error refers to nvidia driver files. I've installed the most recent driver, and even uninstalled all the graphics drivers, to no effect. Hence my theory that this is a hardware problem. The question is, is it the graphics card?
It's not the monitor - that works fine on other machines. But could it be something else, such as the motherboard? I don't know. I've reached the end of my experience.