When you get bored after 30 minutes, instead of starting a game, do some pushups, or some small physical exercise that you can do in the room.
Hopefully it will clear your mind, release some endorphins and you will want to get back to work.
I say this because I had a similar problem and exercise was the only thing that helped.
BTW I'm not writing this as some meathead. I'm a skinny fucker.