I recently had a similar problem with a Rotel turntable I picked up. After getting some advice about it here I came to the following conclusion:

Given the prices of turntables now, it was much cheaper to go and buy a whole new turntable than to fool with it! I messed around with that table for 2 days straight and still couldn't get it to turn the right speed. A new belt would be $25, which may not fix it. If not, I'm out $25. Sending it off for repairs is not an option, just the shipping would cost at least another $20 alone. If it does fix it, the thing still needs a cartridge/stylus. So, I picked up a like new Denon table on Ebay for $40 with a halfway decent cart/stylus. Works perfect!

But I would probably try a new belt if you want to get it running. I just couldn't justify spending $25 on something that may or may not fix it when I could get a new rig for a few bucks more. And if the belt DOES fix it, it's obviously something that gonna go bad again. There's another $25!

Now if it were a $700 Rega/Thorens/Music Hall/Pro-Ject? I'd have spare belts on hand