|If it has been in storage for a couple of years there is a good chance something has worked lose. I assume that last time it was switched on it was working.|
Open up the case and try reseating the memory and video card. Just taking them out and putting them back in can often solve the problem, Push all the internal connectors back in, power supply and data cables to the hard disk.
Then there is always the chance the mice have been at it. Mice do love to chew on electric cables.