It's either a stretched drive belt, or the magnet is too strong (or the drive is just broken!!!)
For the belt, either buy a replacement (can't find the link, but it's a generic belt - google will help), or temporarily "recondition" it by dropping it into very hot water.
For the magnet, stick a small ring (like a washer) of non-metallic material over the magnet, so that it reduces the effective strength of the magnet by holding it further away from the nylon/steel locating disc. I use cardboard from an egg-box carton with superglue to hold it in place.
There are tutorials available, but I haven't saved the links to any of them so you'll have to do a search. For the magnet fix there's a Youtube video - it's actually for a 360 sticking drive fix, but the problem and solution are identical.
The telltale sign of it being the magnet is a loud clunk as the drive closes. That's been the problem on the 4 sticky drives I've repaired. The other telltale sign is if the drive works fine if you leave a CD or DVD in it, and of course that provides a neat temporary solution to the problem - leave a blank disc (or one of the clear plastic protectors that comes with disc stacks) in the drive.