|Wrong forum, should be Windows 8 or hardware forum.|
Could be a number of things from corrupt boot sector, to a power supply failing to a memory or hard drive issue, and possibly others.
Try tapping F8 at boot up and see if you have repair options like:
Last Known Good Configuration
Start Up Repair
or other repair options (I think Widows 8.1 has other options now)
If you do, then try them one at a time to see if any will restore your system.
If you do not get repair options, blank screen, or no signal notice from monitor, you can try disconnecting the hard drive to see if you get a post screen. Then you can see if you try one stick of memory and again with no memory (beep tone). Report all results so we can narrow things down a bit.
You have to be a little bit crazy to keep you from going insane.