I bought my PC in parts and then put it together myself, unfortunately i could only afford a second hand R9280x. the seller told me he had it water cooled and OC'd and that when i bought it he would reapply the fan cooler. but ever since i have had my PC running it has been overheating and i can only run my PC in safe mode and if i put into normal mode and play a game it shuts down. i have run a temp log using cpu-z and the highest temp the GPU got to was 68C and then it shutdown.
MSI 970 gaming motherboard
R9280x twin frozr (i have re-applied thermal paste multiple times)
AMD FX-8350 (cooled by a corsair H100)
hypreX 4gb ram
artic 750watt power supply
PLZ CAN SOMEONE HELP ME???