Dryer buzzing, won't stop heating

Dryer was working. Opened door to get out clothes. Shut door to restart, hit start button & only buzzed. Removed clothes & shut door & keeps buzzing, will not stop. Is not tumbling. Has to leave door open. Top of dryer seemed really hot. Went back over hour later & touched dryer, was even hotter than before. Should have been cool to touch. What can problem be? Bought this dryer used, man said really good. Dried 2 loads & this happened. Of course, man will not ans calls. Any help would be appreciated.