So whats the deal? Is there some kind of limit for new accounts? Is it because of the weekend? His campaign budgets are well over $50....
heyday
Accounts start off with a $50 credit limit if I remember correctly, and increases by $150 each time you hit the credit limit until you get to $500.
So, if your friend is paying by CC and hits $50, there would be an attempt to charge his card. If his CC was declined or has other issues, then the ads will stop showing.
But the easiest way to figure out what is wrong with his account is to contact AdWords support.