eBay won't get involved in warranty claims. Once their own 30 day money back guarantee has expired it's between you and the seller, or whoever provided the warranty.
Regrettably, warranties often prove worthless on eBay. Sellers may claim warranties but when things go wrong many don't want to know. Even manufacturers' warranties are liable to be invalid for items bought on eBay.
Your best hope is usually that your payment provider e.g credit or debit card issuer may be able to help. Otherwise, if the seller is a registered UK business seller you may have some statutory consumer rights - but enforcing them against distant, uncooperative eBay sellers may be difficult or impracticable. There is plenty of information online, or contact Citizens Advice. If they're a UK registered business seller you can also consult trading standards.
These are the risks of buying from unknown sellers on eBay. The user agreement even reminds buyers that "eBay does not guarantee the existence, quality, safety or legality of items advertised, or the truth or accuracy of descriptions". eBay is not like buying from the shops. eBay is a jungle.
