motor sounds fine, no sewing action?

RE:Sears kenmore 158.16031 Given to me a few years ago, was cleaned, tuned-up then and working great.Now it has stopped. It sounds like something is slipping,the needle wont engage when motor is on. I can do this manually w/ handwheel( which requires more effort than usual). the belt around the motor shaft appears intact and in track. It moves freely when I use the foot pedal but nothing else happens. I cant really see or get to the insides. What has gone wrong? Is this a DIY repair? P.S. any idea of this machines' age or where I can get an owners manual?