You are in a tough situation, and it looks like you are gonna have to fight hard.Not yet. Still waiting for UPS to respond to my claim. They said they would Monday. I also filed a dispute with PayPal, just in case.
I'm no lawyer, but I think it might come down to who is ULTIMATELY responsible. In this case, the seller is responsible to get the item delivered in the described condition. UPS, eBay, and Paypal are agents of the seller--not the buyer. You did not contract UPS, eBay, and PayPal to get the computer to your doorstep. The seller did. If I were you, I would hold the seller responsible, including going after UPS.
IMO, the seller will have the right to either ask you to return the item for full refund or the seller may be liable for ALL potential damages arising from current and future claims. Given that you insist on keeping what should have been a "bargain", you'll want to start getting inspections and estimates for how much you want to seller to pay for damage. It's up to the seller then to decide: well, do I want to pay out of pocket or get jerked around by UPS, eBay, and Paypal for days or weeks to come? And worse, I might get a Small Claims Court judgment against me if I don't pay and the judge thinks my poor packaging is at fault, hence voiding UPS liability...
My 2 cents: Continue to pursue all the venues provided for buyer's grievance by eBay/PalPal/UPS. But lay the ultimate responsibility on the seller. You also need to get official estimates for repair in writing in the unlikely event that the seller agrees to pay (whether he pays out of pocket or via insurance coverage).
Simply put, you have a claim against the seller
Lastly, don't know what your budget is, but Apple's refurb goes for $2400.
Best luck out there!