Why is my PC not booting?

That usually means the drive is bad :-(. That said, try to boot the thing by pressing Esc, then select the option to boot from another device - check for the SSD there - I posted a photo from my 645 G11, newer machines always say UEFI - Windows Boot Manager (older ones MIGHT use the SSD/HD model). If you do not see the SSD (it will show the drive model OR "UEFI - Windows Boot Manager), it's either an issue with Windows, or the SSD has failed. You usually have to secure erase NVMes 8/10 times when it occurs, but sometimes you can rebuild the MBR and BCD files to recover them. It's under "Repair your computer>Advanced>Command prompt" once you're in the Windows installer.

It will be one of these two commands, but run both as the older command is helpful:

• bootrec /fixmbr (legacy and UEFI)
• bcdboot C:\Windows (UEFI)

After that, run bootrec /rebuildbcd to rebuild the BCD store. It doesn't always work, but it's that or erasing the notebook with complete data loss.

You will need a USB drive with the installer OR a DVD, so borrow a working PC and make a bootable USB with this guide: Windows 10/11 - USB Installation Media Creation (Rufus)

You should see this on a good machine. If you only see network options, run the WinRE commands I mentioned above on the C drive (type C: in the command prompt, then run them):

If that does not fix it, try secure erasing the SSD - if those commands do not work, the damage is done to the point you have to erase it and accept complete data loss. These HPs make it easy by integrating the secure erase option in the BIOS, but OPAL SEDs will do an enhanced erase by default - and there's NO WAY AROUND IT. Give it 20-30 minutes if it mentions an "enhanced" secure erase because it does not warn you it will do it - it checks for the command, and goes with it first. And 9/10 of these HP notebooks since the G8 have one of those OPAL SEDs as a factory item (or the drive has it in the command set and it's not the SED flavor, and HP's firmware WILL detect it), and the HP BIOS defaults to it when it's available. It's accessed as follows: F10 (BIOS setup)>Security>Hard drive Utilities>Secure erase. You should see this list if you got it right: