First I would check to make sure the video card is clean, and seated properly and nothing came unplugged from it. Computers often won't boot up if something is up with the video card.
I'd also do much the same for other devices. Push on the memory, cards and connectors and such to make sure they are seated. Gently clean the dust out of the fans and such. Don't used pressurized air, you don't need to get it all, just the clumps.
If that doesn't work then it could be a power supply issues or hard drive issue. These are far more likely to go out than a motherboard. I've only had one motherboard go out on me because one of the capacitors went bad, and in that case it made strange high pitched noises.
The memory is also more likely to go bad.