-Get into bios and put any over clocking back to default.
-Run a memory diagnostic to make sure your RAM is not failing by inputting mdsched.exe in cmd.
-Get into device manager and make sure your video card has no errors and update any drivers if needed.
-Becuase the r9 390 is a pretty large card, is it receiving enough airflow?? While checking this, make sure the power connecter to the card and everything in your case looks good.