I recently bought a boat with a Mercury 25HP. Last week when I tested it out the motor ran fine. Only thing I have done since is load it on a trailer. I was taking it out yesterday when I backed it in and cranked the motor. Motor runs fine but the prop will not turn when in gear and the engine revs up. When it is "off" the prop will turn by hand in neutral or in gear. I have a steering wheel and a friend mentioned without looking at it that it could be a broken link in the cable. Any suggestions?