Computer issue, possible power supply issue? could be HDD I don't know

My computer will get to a point where it goes to sleep and won't wake up. I call it "coma mode" it's been doing this a lot.

The only way I can make it turn back on is to unplug it and hold down the power button until I can hear what sounds like a capacitor discharge. Then I can plug it back in and it turns on, loads up and goes right back to where I was. It does this about once every three days.