Cheap keyboards die pretty easily . If the monitor light is flashing it isnt getting a signal from the video card. It could easily be a combination of things like a bad power supply and bad video card. Hopefully the video isnt onboard.

Check the pci/agp cards to make sure they are all seated well. Then take everything out except the video card. This can help to isolate your problem.

Usually when motherboards have problems they let out beeps, it is possible your speaker died. These beeps are pretty helpful in figuring out your problem. You may want to check and/or replace the speaker to get the beeps working.

Lots of other things to check , but I cant remember right now.