Planer problem

I have a Craftsman 13" planer, model # 351.217430. While planing an 8' red oak board, the infeed and outfeed rollers quit; the cutters still rotated as usual. I took off a 1/16th or less each pass. The rollers do not turn, even by hand. I took the case off and looked around; the roller drive chain is intact but I can't move it. The rollers are free of wood chips. The planer has always worked perfectly up until now. I would appreciate any ideas/suggestions on what to look for, because it seems as if a part is broken somewhere and not allowing the rollers to rotate. Thank you, Chris Martin