Maybe a timing issue?

Question

My Singer 14sh654 serger has a problem I can't figure out. When I turn the hand wheel, it makes a clunking noise like metal on metal. When I try to sew, the knife won't cut the fabric (although it's in the correct place and it's sharp) and the thread bunches up on the fabric. Have a suggestion? or should I take it to the shop? Thanks for your help!