Eh, I've bought many a laptop on eBay. In fact, the one I'm using now is from ebay - Thinkpad 600, and got a great deal on it too.
So, essentially what you want to do is such, first email the person. See if they'll agree to take it back. Make sure to save ALL THE EMAILS - their's and yours. It may be important later.
If that doesn't work, you go file a fraud claim. First they'll give you the real contact info, like phone number, and recommend you call them. Try that. Usually it won't go over well, but try it anyway. If that doesn't work, go ahead and file a fraud complaint.
How it works is you'll be placed in a forum with a moderator, with both of you allowed to tell each side of the story. There's no limit to the amount of posting you can do, except once you make a post you have to wait until the other party reciprocates. Make sure to be eloquent - it's helpful to write a test draft first, because this part is pretty important. Don't come off pushy, etc.
If they don't write back you then get into the dealings w/ SafeHarbor or whatever they call it these days. Unfortunately, I think the cap of what you can get back is $500.
You need to mail in your details, your case, and a third party to verify your claim. Pictures are always a plus.
In a few weeks they'll get back to you - you have to state your case again (make sure you stick to verbatim what you filed initially). After a bit of back and forth, they'll tell you how much you're entitled.
As you can tell, I've had to do this before (Not for a laptop). I remained as cordial as possible, and let the seller make a complete ass of himself. It was a $75 purchase - intially they offered to give me $25 back - I wrote back to them thanking them, but reiterating my case lightly, pointing out things they may have missed. They wrote back to me again, and refunded all $75, and didn't take out a $25 fee.
Hopefully it doesn't go that far. This process of mine took six months.
But I did get mine in the end, and he was kicked off eBay.