Within 'International Law' (meaning it applies across the world) if you receive a computer back from a warranty repair, delivered by courier, you are perfectly within your rights to invite the delivery man into your premises so that you can check the [b][u]'MERCHANTABILITY'[/b][/u] of the repaired item(s).
When you sign for goods, upon receipt, you accept that the goods are in full working order.
NO MATTER how disgruntled the delivery person is, DO NOT give them a signature until you are happy with the repair.
In your particular case, if you have internet records of the pick-up, together with 'tracking' information of the return of your computer: I would strongly suggest that you formulate a well-worded email, containing ALL THIS INFORMATION and send it to HP.
Mention at the end of the email, that if you do not receive satisfaction by return email (give them a time limit - 2 or 3 working days will suffice), you intend to copy your email to the Computer Trade magazines and the biggest circulation Computer / IT magazines in your part of the world.
There is no stronger motivation for a computer company to come to heel, than the prospect of extremely BAD PRESS.
I am giving this advice 'WITHOUT PREJUDICE' and suggest that you use these words within the heading of your email to HP.
A Google search for these words will illuminate you, I am sure.