Depending on how long it has been since you won, give the seller time to respond. Not everyone is at the pc all the time, though in saying that if I had an item due to finish i would make sure I checked in.

As you have not paid you at least have no concerns about loss of money, and if the seller has not replied in a couple of days I would send a request to cancel and move on.

Not sure there is much else that can be done, but someone more knowledgable should be along soon with more advice.

tanya, is it a problem with the eBay account or the Paypal account?

If it's the Paypal account then that's a common tactic to try and get the buyer to pay by bank transfer - don't do it because you'll have no buyer protection if things go pear-shaped.

If it's their eBay account is the seller still registered?