EBay provides its own 30 day money back guarantee for most items sold here. After that they have no further involvement. PayPal buyer protection lasts for 180 days, but only covers defects present on delivery. Neither will get involved in faults occurring in use, or in warranties.
Any responsibility now rests with the seller. If they're a UK business seller you should have some statutory consumer rights - but having rights means nothing unless you can enforce them. This is often difficult or impossible for items bought on eBay. Even manufacturers' warranties are liable to be invalid for items bought here.
You can consult trading standards or citizens advice, or consider using the small claims court or the Courts and Tribunals internet-based money claim service: https://www.moneyclaim.gov.uk/web/mcol/welcome.
Good luck, but buying from unknown sellers on eBay isn't like the shops.
