|Sorry, my #2 was nonsense if you can't get to Windows or at least safe mode - I must have been having a bad day. |
You could try turning off the computer then unplugging the tower power plug. Then hold the power off/on button in for about 20 seconds before plugging up again and switching on. I'm not at all hopeful but there's nothing lost trying.
Best wild guess from afar is that the power supply has died - maybe you can get it tested if you are into removing it. Other likely possibilities include the motherboard.
I doubt the HD is died (although it is just possible), so you could fit it in another computer to get your stuff off. The other way is to get an external USB enclosure for the HD (sometimes known as a caddy - quite cheap). Then it could be plugged in and read as a USB HD on any computer.
Always pop back and let us know the outcome - thanks