First a warning, did you use an anti-static mat or wrist strap when cleaning it out.
Did you accidentally disconnect the cable joining the monitor (screen) to the computer (tower). If you are not sure, try pulling out the cable and then reconnecting it. the end to the computer should be coloured blue, or if it's not then it is ages old and probably died on you. Alternatively it might even be a USB cable, try another if it is.
If nothing works, then it's most likely not a problem that you can repair yourself.
Keyhole Kate
February 2012
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