D54250WYK hang/freeze at Intel NUC Logo Page - Tried so many things

I made a small change to the BIOS recently (sound at startup) and my NUC now refuses to boot - always hanging at the Intel NUC logo page. I have tried:

• Moving BIOS Jumper PIN from 1/2 to 2/3.
• Unplugging / Replacing CMOS battery
• Removing SSD / Removing RAM / Only using RAM in 1 slot / Only using one RAM in other slot
• Downloading latest firmware onto USB stick (but can never get the USB stick to basically load the BIOS recovery)
• Long pressing the power button with the CMOS battery disconnected to discharge
• Tried using miniDP to DP on one monitor, and mini-HDMI to HDMI on a TV.

Additional Info:

I managed to get in BIOS once (not quite sure of exact steps) but I reset to defaults / F9 and saved, but still nothing then worked - still froze on NUC logo screen.

One time I managed to get to the GRUB menu and it launched into booting Linux Mint but it got a Kernel Panic.

Sometimes the CPU fan spins / sometimes it does not. Sometimes it won't POST at all (slow flashing light). Sometimes it's showing a solid blue light but nothing at all on the screen.

Sometimes the F2 Setup / F7 text appears in bottom right hand corner of logo screen, but can't replicate this many times.

Sometimes with the USB stick in the port, it will say "not bootable medium" (the USB is FAT32 formatted with MBR).

As further background, I was using the NUC with a GRUB menu (Windows 10, Linux Mint and Batocera) - Linux Mint defaulting after 5 seconds if nothing selected. Everything working without issue until I changed that one setting in BIOS!

I think essentially the NVRAM is now in a bad place, and the Boot Order is completely screwed / some kind of partially reset but not fully reset stage or something crazy.....but I cannot find for the life of me find a definitive way to reversing this issue.

I feel like I have verified all the components - CPU, RAM, SSD, Wifi Card are all still working, but the BIOS / NVRAM is corrupt.

Any help would be appreciated - some kind of final checklist or correct order to salvaging this.

Thanks!