Your RAM memory is faulty , This causes the computer to restart , Change it and then see. Generally these assembled PC sellers sell used RAM / 2nd sale RAM which are faulty 60% of the time , Insist on a brand new packed RAM stick from kingston or transcend, and check whether it is in its original seal packing. It will cost a little more.
Does your computer crash randomly or only when playing 3D games and Installation
If it crashes randomly its more likely to be a problem with the PSU. What brand and rating PSU do u have. You could also perform a Memtest to elimnate your RAm as the culprit