Hi, unfortunately many sellers of mp players on eBay are scammers who sell players with hacked memory. The first thing I would suggest you do is follow the instructions posted here:How To Removing a Memory Hack
If the memory turns out to to smaller than advertised, the second thing, since you bought it off of eBay, is file a dispute through Paypal (if you paid that way) stating the item is not as described or non working whichever the case may be.
How are you putting the music on the player? Most you can copy and paste the music directly to the player and do not have to use Windows Media or iTunes.