Ferrum :
My newly build computer just keeps randomly restarting itself and i have no idea why. It just randomly shuts down without any warning and then starts up again. I checked the temps and those seem fine...
So i really have no idea on what to do...
First you should try to reinstall you operating system.
Assuming you have done that you can try the following steps.
Step one.
Disconnect DVD drive. (test for stability)
Disconnect all other external components that are not essential.
remember to also remove the USB disk, mentioned under Storage devices
Step two.
pull out one of the ram modules. (test for stability) Running with only one module will check the Ram.
retry with the other module.
Step 3
If possible try with other PSU (test for stability)
Step 4
Run the PC with the stock GPU - disconnect the Radeon R9.
Step 5
Assemble the components outside the computer chassis (to check for short circuit)
Step 6
Make sure you don't use too much thermal paste on the cpu - it can dammage the MB.