Find the item in your My eBay Purchase History. On your order there is an estimated delivery (do bear in mind that this is just an estimate).
If it's way past the estimated delivery date you should contact your seller.
If no joy, you are covered by eBay's Money Back Guarantee and can open an item not received dispute.
Read up on ebay's Money Back Guarantee here:
http://pages.ebay.co.uk/buyer-protection/faqs.html
