That sucks man. A few months ago I was having similar problems where everything worked but nothing showed up. It turned out that my MOBO was shot because some of my liquid coolant got into the PCI port for my GFX card and everything died.
If you have integrated graphics on your MOBO or another GFX card, try hooking your monitor up to that and taking your GFX card out. If it works then that pretty much says its the GFX card.
You haven't made any recent hardware changes have you? Sounds like a dumb question but I was working on a friends laptop and I took the ram out and popped it back in switching the two chips on accident and the thing wouldn't start if they weren't in the old slot.
As for ruling out the CPU, I'm not really sure what to say. If it was overheating, it would shut its self off, so it's probably not a heat issue(probably).
Check out
http://www.tomshardware.com/ you can pretty much ask a tech question about anything and it will be answered within a few hours usually. If the little ask a question box wont work, go to the forums because all the ask box does is post it to a board.
Good luck!