make sure that all the lint is out of it. if it gets lint up in the ductwork behind the lint screen, it will not dry worth a crap.
also check your breaker to make sure it is not half tripped...your dryer breaker is a two switch breaker that is bridged with a metal bar on the handle. you might have one side of the breaker trip and not the other, allowing the dryer to run but not heat up.
if it is putting out air and it is not hot or is only warm, you might have a bad or two bad heating elements. if you can get the cabinet off where you can access the terminals of the elements, you can test them w/ a continuity checker or ohmmeter. if they have continuity, they are good, and your problem lies elsewhere. while you have the cabinet apart, check to see if there are any fuses or fusible links that might be blown.
If any fuses are blown, find out why. it might be that you have lint build up in the dryer not allowing proper airflow and thus overheating the dryer.
AJ