Hi kuchen85,
If you really want to get the seller's attention, file a DISPUTE with PayPal and ask for a refund of the product because it's faulty. I bet you you'll get a reply pretty quickly!
How long have you had it? It might be a good idea to start the process of a dispute with PayPal to get a partial or full refund of the player if it's faulty and while that's under way, look at a way of 'repairing' your player.
Does Windows recognise your player at all? Can you transfer music to it and such?
Anyka firmware maybe slightly harder to work with as there isn't many information available out there. There are a few to download from this site but I just don't want to see your player in a worst state.