PC wont boot anymore?

While working on my PC, it suddenly rebooted. I didn't think much of it, so after it rebooted, i just continued using it, but then the screen froze, i couldn't move the mouse, not even turn the caps lock lamp on. So i turned of the power supply switch of and on and started the PC, the fans rotate, but the monitor and the keyboard lights don't turn on and no beeps. I tried more time to turn it on, and succeededd once but it only got to some text telling me that CMOS is wrong (the battery for my BIOS went empty) and then froze again like before, and now i cant even get to that text when trying to start.

Does any1 know whats wrong?