My display driver stops responding, then recovers, but half of my objects then are invisible. Does anybody know what could cause this and how to fix it?

Reinstall or update video drivers.

To fix them being partially invisible, try hitting A twice to toggle lights. I know sometimes if I minimize the geck, things will dissapear, so its probably this. If your video card frequently does this then do what Echonite said and make sure your video drivers are up to date.