If you want to take a stab at fixing your computer problems yourself, here is a list of steps and things you can try.
Quit. Quit all running programs (see the tip on using Ctrl-Alt-Delete below). If the problem persists, restart the computer.
Turn on. Make sure everything is turned on. This means your computer, monitor, speakers, printer, and anything else connected to your computer. If you call a computer help desk, the technician's first question will be: "Is everything turned on?" Many mysterious crashes are solved when users check the on switch. If you're having problem with a peripheral (printer, scanner, modem, and the like), try turning everything off, then turn the peripheral on before turning on the computer.
Check the plugs. No matter how little you know about computers, you know how to plug something in. Get behind your computer and get to know the cable spaghetti back there. Make sure all the plugs are securely seated.
Check the hardware settings. Is the volume turned all the way down on your speakers? Is the contrast on your display turned all the way down?
Check the software settings. This is a little more complicated, but if you get to know your Control Panels, you can fix many problems. For Windows 95 users, check out the Device Manager.
Take a peek under the hood. Learn how to remove the top of your computer case. Check to see that everything's plugged in and cards are properly seated. Before you mess around inside, ground yourself (touch something grounded).
Clean house. Give the computer a good cleaning, inside and out. A can of compressed air (available at any electronics or computer store) is great for getting rid of dust, but you can just use your lungs. Just don't tell anyone from tech support that I recommended you do this.