Most generally the problem will be a burnt out heating element, but the second most likely cause would be a bad thermal fuse. There are usually 2 of these fuses mounted near the heating elements, they are silver in color, and about the size of a quarter. All can be tested with a continuity tester. The heating units are aboy $15 -$20, and the fuses are about $5.00. Unplug the dryer before testing the units.