In the last few weeks we have suddenly been unable to use our desktop computer at home. Every time the computer turns on a box appears on the monitor saying no VGA input and puts itself to sleep. What could the problem be and what could have caused it? Is it the monitor, cord or something else? We have tried everything to make it work. All of the cords and such are securely placed and there's no evident damage anywheres. The computer is 3 years old and an HP.

Is it the monitor, cord or something else?

Could be any of the three. Beg or borrow another monitor to determine if the problem is the monitor or the video output of the computer. Cables are rarely a problem unless they have been abused. If the computer appears to be going through its normal startup routine with beeps, noises, and the hard drive light flashing, it is probably the monitor. If the computer once powered just sits there and the drive light has no activity, the computer itself is suspect. Also, if the monitor has multiple inputs, confirm the wrong input wasn't inadvertently selected while dusting, etc.