Monitor shuts off but everything else keeps working

Hey i have this problem when like i downloaded prototype cus i wanted to play and i play for like 5 min and my monitor shuts off but everything works properly.I had this problem in the past when i thought that the problem was overheating but im not sure. It might even be the monitor cus like 2 years ago my window suddenly oppened and it hit my monitor and then smoke came out of it and im like what just happend (it was realy windy that day :/ ). So i think that thats the problem i dont realy know. Can someone pls help fix this like on my own or should i go and fix it at a pc shop or something.
Before the "accident" that i had with the monitor it didnt shut down and when i start the pc the fan that is under the big box that is for the power and something it doesnt spin so i have to give it like a push or something to get it to spin so i dont know why is that i cleaned it and got the box out removed all the screws and i cleanead it but it still does that so what should i do. Pls can someone help me fix this :D :D
P.S. The monitor shuts down after like 5+ hours of the pc being on and like 10 min if i play some games (i play minecraft so on mc it lasts like 2 maybe 3 hours)