Few things it can be:
1) CPU/GPU Overheating -> Watch temperatures for both with an application like HW Monitor
2) HDD Errors -> Check with 'scannow /sfc' in cmd
3) RAM Errors -> Check with `mdsched.exe` in cmd, then reboot to run test
4) Bad GPU Drivers -> Update to latest
5) Power supply dying -> Not really a way to check.. so do all the other tests first.. if all others are OK, this might be the problem