I recently sold an ATV on ebay and finally received down payment into my PayPal account.  However, the  buyer on three occasions has not picked up the ATV as he promised.  Nor have I seen a bank check for the balance.  I can email hin and phone him but he no longer answers.  The partial payment was received from a hotmail email address which I've emailed, but the email was undeliverable because no such mailbox exists, yet I did receive the payment.  I think the buyer is a middleman for someone in Europe, and that person paid.   The ATV is just sitting here.  I need to get this resolved.  What should I do? 

"Europe", "Middleman"? Loren is right about the check. Almost certain to be a counterfeit.
This has all the signs of a 419.
Hang on to that "down payment": it may have come from a stolen CC, or hacked Paypal account, and PayPal will soon be taking an interest in the matter.
Again, excellent advice. Check e-bay's policy on defaulted purchase - and maybe put them in the loop - before re-posting the item for sale.
Good luck on the sale - and on avoiding future guymen(Nigerian slang for 'con artist")