sudden failure

Hi, my PC suddenly started not POSTing giving no beeps and not showing any video output. The PC was working fine the day before this happened I didn't make any significant software or hardware changes. This already happened in the past, but I fixed it changing the PSU so I'm excluding it from...

I'm not sure why this is happening. The day before it was working fine, then I shut it down and went to sleep. The next day I tried to turn it on, but it doesn't boot or post. The red light on my motherboard turns on for a very brief split second then then off, and that doesn't happen everytime...