There's no debris or wood jammed in the housing around the blade, is there? Try unplugging and removing the blade, to make sure some wood hasn't gotten wedged in there somewhere.
Otherwise, make sure the blade is on tight. If so, there is likely a problem with the motor itself.
If it's still under warranty, I'd contact Ridgid at this link:
http://www.ridgid.com/Tools/Support/
Otherwise, they have a tools forum where you might be more likely to find someone who's experienced a similar problem.
Being reconditioned, it sounds suspect to me...
Sorry I couldn't be any more helpful...