First check for infections. Download the trial version of malwarebytes and scan your computer. Download ccleaner and run cleaner and registry cleaner. Defrag your hard drive. Most of the time I find with a malware infection antivirus will simply not pick it up. Upon boot scan usually there is a pagefile virus adjusting the size of your pagefile constantly (slow down). I have seen many shops try to remove malware infections and then their customers come here. Lol. Once you have an infection malwarebytes will not be able to remove it. Malware zips itself up in the file system making it difficult to detect and remove. I usually save the customers data and wipe the drive reinstalling the system.

Hook a monitor to the VGA port on the side and see if the video works. If not it is likely your video chip on the board is shot (Bad Motherboard). If you have clear video then it is most likely the screen. If it is the screen you can find the moderately priced on ebay.