First of all, check to make sure there aren't any unshielded speakers or halogen lights near your monitor. These can really make your monitor do weird things. A television, audio receiver, or other electronics equipment nearby can also cause interference with your monitor because of the frequency of the signals they use. If there is nothing creating interference with the monitor, check the cable connections and make sure they are nice and tight. Also, try and get your wires as untangled as possible.

If none of these things seem to be the problem, your monitor settings may have been reset and you may have to make some adjustments using the control knob or buttons on the front of your monitor. The things you may need to adjust are your color settings, the convergence, and the moire settings. See your monitor's manual to see how to adjust these options.

Finally, if you monitor still won't show a clear picture, something may have gone wrong inside it.

Unfortunately, there's not much you can do to fix a bad monitor other than take it in to the shop. Before you do that though, see if you can hook the monitor up to another computer. This will help you determine if the problem is with the computer's video card and not the monitor.

Remember: Never open a monitor and try to fix it, as the electric charge stored inside it can be extremely high and very dangerous.

For a desktop computer, if you're using a Mac or running Windows 98 or later, you can hook up as many monitors as you have video cards. Basically, you need a separate connection for each monitor. So if you had 3 PCI slots open, you could add three video cards and three monitors, allowing you to have four total screens. Some video cards have connections for multiple monitors, which would allow you to connect even more displays to your computer. (These cards usually support 2 or 4 monitors apiece.) I've heard of a Mac that ran 14 displays at one time, which is just ridiculous, but nonetheless, cool.

This happens when your screen resolution is set to something higher than what your monitor can display. For example, if your monitor supports resolutions of up to 1024x768 and your video card allows you to crank it up to 1600x1200, doing so will give you an error. Another reason you might get the error is if the refresh rate you selected a certain resolution is higher than what your monitor supports. The monitor can't "sync" with the video card, so it just gives you that "Out of Range" error. If you are sure you have your resolution set at a reasonable amount, make sure that your monitor is plugged in all the way. Actually, if you're like me, that might be the first thing to check. =)