I dont get it

Hello,

So i have this very very striang issue going on with my system. every so often when i am doing someting on my computer or after a software update and a restart my monitor will go black and say it does not have a signal. After it does this if you push enter the computer will restart and then either stay in this loop or allow me to go back to my desktop without any problems. The problem seems to be completely random in nature. However i play alot of online games and had a issue when i was playing were the graphics went all weird. Thinking that i had a issue with my graphics card i grabbed another one i had laying around and switched it out. A few minutes later another issue came up with the graphics so i figured since i had used two different graphics cards with the newest drivers and such that the issue had to be Motherboard related. So i purchased a new motherboard and installed it, reloaded windows and the motherboard drivers. When i went to update the drivers for the better of the two graphic cards and restarted the same issue i described at the beginning of this post was present again. any idea at all this one has me stumped