Mac Book Pro Won't Wake

[Mac Noobling]

So I have a 2011 15" mac book pro and it was sitting closed in my living room for a number of hours in sleep mode. So later when I went to open it it didn't respond to anything I could hear the fans going. I tried to try up the brightness it didn't do anything. So I held down the power button till it shut down. When I rebooted the computer everything seemed ok. I even tried to close the lid for a few seconds till I herd fas shut off then reopening it and it worked fine. The mac has done this once before and the only thing that I can think of that is causing it is that I downloaded Civ 5 from steam the other day. The day after I installed it the computer took a number of minutes to boot up and recently it has had this problem. What do you think? Thanks!