I can't get the setting on me other PC above 16 colours and 640x400px...

Why? It used to be a reasonable setting, but since I got it, and reinstalled Windows, (and removed all the old stuff) I can't make it work properly.

I've tried plugging in this monitor, and using the drivers etc. off this computer, but it makes no difference...

Monitors don't really have driver disks, AFAIK, so what's gone wrong?