Saying the serial number on the back of my hp pavilion 23-b320 is invalid..

[Spacedad41]

The hard drive on my hp pavilion 23-b320 failed so I ordered a new one. Installed it, now there’s nothing to load when I turn it on. I assume I need a boot disk to load windows. I came here to attempt to order one but it says the serial number that’s clearly printed on the back on my computer is “invalid” when I type it into the website and chat. 

[Paul_Tikkanen]

HP no longer sells recovery media for your PC.

The only place that I know of where you can order recovery media would be from this vendor:

Computer Surgeons - Windows 8 64 Bit (13AM2AR8602) Recovery Kit E1L99AV (USB) For HP Pavilion All-in...

There is a way to reinstall W8.1 for free if you have another PC to create the installation media with:

Install W8.1 by creating the Microsoft installation media, using another Windows PC...You want W8.1 64 bit. 

https://www.microsoft.com/en-us/software-download/windows8ISO

I have zipped up and attached below, the free Rufus utility which will transfer the ISO file to a USB flash drive, so it is bootable.

Rufus - Create bootable USB drives the easy way

Set up the Rufus menu exactly as you see it in the illustration for Windows installations.

Boot from the USB installation media you created with Rufus.

If you are asked to enter a product key during the installation process, use this generic key.

This is the generic key for W8.1 'standard.'

 334NH-RXG76-64THK-C7CKG-D3VPT

If you had to enter the generic key, manually change the generic product key to the W8 'standard' key in your PC's BIOS in the PC settings menu.

After you get W8.1 installed, and you had to manually enter the generic product key, you will need to run the free utility I zipped up and attached below, that will show you show the W8 product key in your PC's BIOS.

Then you can install the available drivers and software from your PC's support page.

HP Pavilion 23-b320 All-in-One Desktop PC Software and Driver Downloads | HP® Support