You will have to take it apart and see if the belt is moving both pulleys it's on, or if the motor is stalling, or pinch roller not staying on, hardened rubber or broken spring, etc.
Is the player worthy of buying parts for? You might find something that works, cheap at a garage sale, craigslist, or pawn shop, or sometimes I shop for *local* (pickup) items with no reserve auctions on eBay. Last bookshelf stereo I got for $0.01... but without the remote control, which I ended up paying someone else $10 for.
