Crash

So around every 7 games or so, my whole computer just freezes(mac). My League and everything else just stops, including itunes music and stuff, but league music still keeps on going. My computer won't respond to anything in this time. Ive even tried restarting the wifi. When I disconnect my monitor and open my mac(it is connected to a monitor), it stays black. The only thing that responds is holding the power down button and restarting my computer that way. I keep getting into lower prioirty queue. PLS HELP! I CAN't STAY IN LOWER PRIORITY FOREVER OVER AND OVER AGAIN!