Monitor settings

You most likely lost the video card driver.

Identify the make and model of your display adapter (video card) and download the latest driver.

I also recommend re-installing the driver for the chip-set on the motherboard when this happens.

Ifyour's is a name brand system, you should be able to download all the drivers from the manufactures web site.
Otherwise, if you need help identifying your motherboard, check out the ID tools at either www.motherboards.org
or www.wimsbios.com

Install the drivers in the following order:
Chip-set driver
DirectX (from Microsoft)
Video card driver
Monitor driver if the monitor is not listed among Windows supported monitors.

You should then be able to set your display colors and size as desired.

Chas