Dryer won't heat

I’ve had this dryer for 3 months, and everything seems to work fine, except that it doesn’t heat. Anyone? It was working fine until today.

I bought it at a discount appliance store, does that invalidate the manufacturers’ warranty? If the warranty is still good then I don’t care what the problem is.

If neither breaker was tripped, does that mean they’re OK, or can one burn out and not trip?