UPS is supposed to make 3 attempts; did they ever leave you a door tag? If they did, and you never responded, then it's your own fault, but if they didn't make 3 attempts, or never left you a door tag, you've got 'em by the balls. Call 1-800-Pick-UPS and wade through the automated system until you get a real person. If they didn't do what they're supposed to, then don't take no for an answer, but if they did, be really nice, and you may be able to get them to re-route the box to your work address, your parent's house, your buddy's house, etc. - But do it immediately - if they get the box all the way back to the shipper, they will definately NOT re-route it, and then you'll have to deal with the seller, who'll probably want you to pay for repeat shipping.
Good luck!