My guess would be that they're too tight. The OP didn't mention if
there was any squealing or not. In my experience too tight doesn't have
any immediate symptoms but can lead to loud pump bearings after a
while. While loose belts tend to squeal.

What happens after you're done cranking? Does it quit? Does it even
start? In either case, need more info and you're belts are misadjusted
(whether tight or loose).

- Justin