Computer crashes randomly while playing video games.

I got my custom built computer for Christmas of 2014. My computer is relatively new compared to other computers but recently (past couple of months) I've been experiencing one a bug that makes me unable to play games for very long. What happens is that whenever I try to play a game every 30- 120 minutes it completely stops working and I have to hard restart. I have waited quite some time and pressed all of the button combos that should stop the game I'm playing but nothing happens. I have tried many thing like checking for viruses and updating my drivers and even updating optional updates for Windows. I use Windows 7 Pro. I have even tried removing my RAM sticks which I thought to be corrupt. Before doing this though my computer could only handle 10 minutes of the simplest games like Garry's Mod. After I took one RAM stick out I played one of the first games that started to give me problems (Payday 2) for about and hour and everything seem to be fine. For a while everything was and I played crash free that is however until yesterday (today is April 19th). My computer crashed once again. Today while I was playing it crashed 3 times each at a random length of play time. So I then decided after the second time of crashing to switch the RAM stick but at the same time still only having one in. My computer was a little slower but I think that's because I switched. Although maybe they're both corrupt, I don't know. So I have been given many theories of what could be wrong. One that I think might be the case is both RAM sticks are corrupt. Another one of my theories is that it's overheated, although I don't know how hot computers are supposed to get while playing games for long periods of time. Another theory is that my Windows is outdated. I don't know if this would cause my computer to crash but I really don't know at this point. The final and I think least possible theory is it keeps disconnecting to the internet which causes the computer to overload or something. So if your reading this please tell me what you think I really want to play without any problems so if you have anything please tell me. Sorry this is so long I just really want to get to the bottom of this so I want to give as much explanation as possible.

So this is the second time I've posted this and now I'm writing an update. I've now upgraded my Windows to 10 and this hasn't fixed the problem. Before I did this I did 4 stress tests and I got a good score for all of them, so I know it's not the CPU or GPU. Earlier today I took some canned air and cleaned out the RAM sticks and slots of dust which seemed to work until a few minutes ago. My computer once again stopped working and I had to restart it. So now I have no other options so I'm hoping someone here as anything. So if you do please tell me. One more thing I think I should mention is that I'm usually in a Skype call so maybe that could be the case but I have played alone before and it has shut down anyways.