Just had to reformat hard drive and installed Windows XP professional. Now I can't get my screen resolution to change over the 16-bit. Everything on my screen is too big. It seems like the computer doesn't recognize the monitor now. It is the same one that came with it originally. Have tried searching Dell site for drivers with no luck. It is a Dell Dimension 2400 desktop. Any help will be appreciated. Thanks.

It may not be a problem with the monitor. You might want to check your video card driver. That is usually the bottleneck for graphics. When you reinstalled it may have given you a generic driver rather then a specific one. Id look there first.