" crashes constantly " when does your PC crash ? Playing games ? when your PC is idling ?
" maximum gpu usage was about 78% " when was it about 78% ? Playing games ?
Can you run memtest86+ just to see if your RAM sticks are bad and HDD diagnostics to see if you have bad sectors ?
What OS are you on ?
What version CCC do you have installed ? If you switched from CCC 9.xx to 10.xx, please be advised that there are driver module changes between versions. Therefore, proper uninstall and re-install is a good idea. Do what mosox said above.
Please check if your PSU is of specification v.2.2.
Hope the above helps.