Craftsman riding mower won't move forward
my craftsman riding more (10+ years old) will start, run, engage the blades -- however, when i put it into gear it won't move. As far as I know, nothing bad happened to the mower -- when I last used it, all was well. When the mower is turned off, I can freely push / pull it while it's 'in gear'. Any suggestions on where to start looking?