[ocellis]

I suspect a failing harddrive. The "lags" probably resulted from I/O operations timing out. Since you apparently were able to select the "Boot into Safe Mode" option, the BIOS must have been successfully loaded, which makes CPU or mainboard problems unlikely.
Graphic card problems would have presented themselves as artifacts on the screen before the reboot, and RAM issues would have resulted in BSOD.

I would remove the harddrive, connect it to whatever computer you are currently using, and backup as much data as you can. Don't write anything to it, and stop trying to boot from it.