I have a 250 4 stroke that wont turn over at all. The starter works fine,but its not turning the engine over.  

have you checked to be sure that it is getting spark at the plug?

make sure it is geting spark and we'll go from there.  

Ok, Its getting spark. I just put a brand new spark plug in. When I push the start button, the starter turns over. But the engine does nothing.You just hear the starter spin.  

If the engine is not turning over but the starter is, then the starter is not engaging the flywheel.  Could be the bendix not pushing the gear on the starter into the flywheel.  Worst case, the teeth on the flywheel may be damaged.  Was there any history leading up to this event?  

I bought it from a friend for $500. It didn't run when I got it, And the engine is still factory new! He said it just stopped working. I think you might be right about the flywheel though. The gears are still new,but for some reason they aren't touching.  

some starters have a secondary gear, and some have a starter drive chain.

check to see if the drive chain or secondary gear or flywheel are bad.

some of the chinese atv's have a drive chain, they have a bad habit of breaking or coming off.  

I'd go with the bendix is bad  

Alright... Well I will check the bendix,and the starter chain(if it has one). Thanks for you guy's help!