It could be your heating element in your dryer has gone out. You can get replacement heating elements for dryers for pretty cheap.
Then again it could also be an electrical problem in your breaker panel causing your dryer to only get 120 Volts vs the 220 Volts it needs to operate.
I had an electric dryer not heat up before and the heating element was fine. Turns out that for some reason the dryer was only getting 120 Volts from the breaker panel.
I believe the electrician said the 220 Volt circuit breaker was bad on one side and not sending the other 120 Volts on the second wire that the dryer needed.