The lights are on
When you fire up the Computer do your fans ever spin at super high speed almost like a jet engine? I had this problem with my Dell Desktop. Turns out the capacitors on the motherboard had bulged and leaked. When you open the case take a look at the tops of the Capacitors (they should be perfectly flat, most have a cross on the top of them to better view the flatness). In case you do not know what a capacitor looks like just google it. Otherwise they are cylinder shaped and some are rather large and usually lined up in rows. otherwise it would have to be the vid card or possibly your bios is corrupted. If you have a backup video card (maybe a friends you could borrow for a test) or onboard video try that out.
good luck to you