hey guys i just bought a prebuilt recently on craigslist and am currently trying to upgrade it but running into a problem. Sorry if this is the wrong sub idk where to post, i have a GA-78LMT-USB3 mobo AMdfx6300 cpu and gtx 950 gpu with 8gb of ram and slow as balls 500 gb western digital 5400 rpm HDDand a shitty Chinese knock off 500 w psu. the pc came with a gt 720 all ive done so far is add a gpu and i can play games at okay frames but after an hour or so of gaming (rust/ bf4) the pc just shuts down like someone flipped a power switch, no bsod nothing, just reboots like nothing happened. i cant figure out whats causing it, it doesnt seem to be a crash, my temps look good usually 70 c for cpu and 60-65c max for gpu. idk any help is appreciated.