Welcome to the wonderful world of today's eBay, where there in no penalty for bidding and not paying for a car. If it has been a week since the auction ended, and you have no contact from the winning bidder, assume that they are not going to follow through.
EBay will not even refund your fees on a vehicle sale. They make their money and do not care if you get paid.
Put the car on Autotrader.com, and on Craigslist to sell it
In your original advertisement did you stipulate how long after the sale the car must be paid for? If not this could be a problem. Always give a time limit for the transaction to be completed.
My suggestion would be to contact Ebay and tell them the buyer has refused to make contact after your attempts and see about relisting the car at no charge. You can also ruin his credit on Ebay by turning him or her into as a bad bidder.
Have they paid for the car?
If they have not paid then file a non payment with e-bay. If they have paid then stay calm it is now there car. And it is up to them to pick the car up. If you have e-mailed them and letting them know that the car must be picked up by a certain date then if the car is not picked up then they will forfeit the funds and you can resale the car.
Look for someone else to sell the car to, you can't wait around forever for this one person.
Clearly they're not interested if they won't even try to stay updated with you on the status of the car.
Now if all they did is bid on the car then it's not sold yet. However, of the auction has ended & they have not paid or communicated after three days, then I would be worried. If they completely fail to conclude the transaction, then report them as a deadbeat bidder & you'll have to start over.