I am 99% sure that it is the PSU. The thing is that like a month ago I was using the computer with its native HDD. I was downloading a lot, like 3 days without stopping and one morning I woke up and computer was down. I always leave it for the night to download. I tried to power it up, and it did except that the monitor was black. So yesterday I switched the video cards and everything went fine. I think that the PSU fried my video card too!!!