When you reinstalled XP you likely did not reinstall the proper drivers.
If you are using a default driver the resolution is terrible and you can not change it with the slide bar in display settings.
You will need to install the video card driver for your specific video card. If you have the CD handy you are set. If you do not have the CD or do not know what type of video card you have you have a few options.
1. go to Device Manager and look for something with a yellow exclamation point. This is hardware that does not have the proper drivers installed, try to let windows find the driver for the device.
2. go to the manufaturers website for the computer if you bought a computer retail ie Dell, HP, Sony, Gateway, ext.. and have not changed the video card. Go to the support link and chose drivers or downloads. You will have to select the model of computer you have and then download and install the drivers. The exact web address is different for each manufacturer so I would google search to find it.
3. If you added in a video card and lost the CD you can go to the video card manufacturers website and download the driver from the support link. If you do not know the type of video card you have, open the box and look. Most video cards will have a small sticker or printing on the card with a model number and will clearly show the manufacturer of the card.
