You can transfer iTunes purchases from the iPhone to the laptop.
Launch iTunes on the HP. From the menu bar top of the screen click Store > Authorize This Computer
Connect the iPhone.
From the menu bar again, click File > Transfer Purchases From ...
You can do the same procedure on the new Mac and you will have to "authorize" that computer also.
If you can't locate the external drive, when it's convenient, backup your iTunes purchases > How to back up your media in iTunes
I'm sorry you got ripped off... that's awful.
Carolyn's advice is good as usual but it doesn't cover music not purchased from itunes. Many of us have lots of CD's ripped into itunes, for example.
I bought a piece of software called Touch Copy which treats the iphone/ipod etc as an external drive from which you can copy your files to wherever you want. It's not expensive and it's saved me twice from losing stuff that I'd not protected/saved properly.