If you reinstall the OS, you need to reinstall ALL drivers from the Dell driver CD that came with the machine. If you don't have that, use your service tag to find the right ones on the Dell site.
Will make a big difference!
My computer has had XP3 reinstalled and I can't get a satisfactory display, currently 640x480. I've tried control panel/display/settings but the slider won't budge. When I right click the Desktop and adjust display settings, the screen goes black and all the lights on the Dell monitor flash and the only way I can turn the machine off is to press the power button. When I start up again, the lights are still flashing.
I then tried safe mode - slider won't budge, machine re-starts with flashing lights.
Help and advice would be very much appresciated