unplug the cables going into the Hard Drive and Graphics card, Let it cool down for a while, and then reboot
this still sounds like PSU error.
1. check motherboard for "bulging" capacitors
2. make sure all fans and heatsinks are clean and working.
3. run Memory Test
MemTest - click here
Tutorial: How to use Memtest - click here
Windows Memory Test - click here
4. download diagnostic prgram from your hard drive manufacturer and run full test.
1. run a good virus and malware checker
2. check there is plenty of spare space on your hard drive for the "swapfile"