Why do the blades stop working on their own? Dixon 4515B?

It was working great yesterday, then today I tried to mow and the blades quit mowing. The belts look fine, I cleaned all the mulch away from the pullies, Then I couldn't get it started because of the battery being dead, so don't know if I fixed the problem or not. But just in case I didn't fix it, is there an adjustment I can make to the belt, pullies, or deck that would fix it? I should go to lawn mower school!!