Please notice this kind of thing has never happened to me, so this is just my opinion, things I would do.
You need to prove the courier got your computer. As always I would like to assume people are honest, the courier in question, too, so I would first try to contact him. Try to remember the exact date and time when the courier picked up your laptop. Then call the courier company to ask them to tell the courier to contact you, leaving them your phone number and email address (I doubt they'll find him to receive your call).
The courier should remember you and receiving the laptop if, as you told, you did not even pack it. In this case I do not believe HP is going to compensate you, instead I believe you would be compensated from the insurance of the courier company.
If the courier says he can not remember, or if you can not in some other way prove the laptop is already picked up, the worst case scenario is you have to report this to the police as theft. Then it is your word against the courier's / courier company's word. In this case I think you'd better to buy a new laptop.
Very sorry for you,