sounds to me like either your GPU has failed, or your PSU is failing and not powering it sufficiently. do you have another PC to try your GPU in to see if it works? If you can do that, and works, the PSU is likely to be a problem, however, if you can do that and the GPU DOESN't work, then you're in need of a new GPU.
Well, if you have a friend with a PC you can try it in would do it. Another thing to try is if you have another GPU, try it in your current PC. Whatever the case, the GPU is my first guess for whats wrong.