Not Installing

It kept saying I didnt buy it after waiting 5 hours over and over, The First time I downloaded it my macbook shut off because of low battery, The second time I waited for the full thing to download (AGAIN) and it said something about Failed to Verify Purchase please reinstall at the app store, So I do that. And what do you know another 5 hours goes buy… Same messege…. Im going to try one more time if it doesnt work this time then I dont know what to do…. Does anyone have a solution to this problem?

Tevernden about Batman: Arkham City GOTY, v1.0