My HTC Droid DNA is restarting on a constant loop!!!!

[jtkoon]

So it started a few days ago my droid dan started restarting on a loop. Just flashes the htc logo vibrates and then goes black again and again. Most of the times it stopped when i banged it on the table a few times but this time it will not. I can't take out the battery or do anything to stop it. I tried holding down power and volume down and the screen popped up but then in a second when back to the htc logo. Need help quick