I need help!!!!!

I need help with a problem that I have had for some time now. I am currently rooling with amd fx (tm)-8300 eight-core processor 3.3 ghz. I used to have a AMD graphik card but switched to an NVIDA GEFORCE GTX 750 TI. The problem is that my pc Shuts down when I play games. It's like the power gets cut from it since when it shuts down I cant start it manually and need to wait around 1-3 min for it to start up again. The heat is about 35-37 when I start up the Pc and slowly goes up. The wierd part is that the heat does not go over 50 sometimes. I really need help with this :C