Dell 1520 Laptop, Intel T2370, 4GB RAM
Linuxmint 21 cinnamon live DVD won't boot.

Error: incompatible liscense
Entering rescue mode ...
grub rescue>

Tried on Desktop Optiplex 780
Intel Core 2 Duo
4 GB RAM
Error out of memory
Entering rescue mode ...
grub rescue>

Burned DVD using K3b at 4X. K3b reported Success.

To me it looks like corrupt DVD indeed, or corrupt ISO. Did you verify its integrity before burning?

I did verify. I suspect the .iso as per instructions.

I suspect I have a BIOS problem, maybe need new battery. My laptop is 16 years old. The bios settings had reverted to default (Battery) I changed them to boot from USB drive first but still no luck. When I booted to the usb DVD burner/drive the computer only saw it as an internal DVD device Which was non existent and not as a USB device. "Computer" icon does see the USB DVD drive as such. I Loaded installed 21 onto a USB stick and was able to boot to it and run a live session. Will try the USB DVD drive on the desktop computer to see what happens.

Yup. A new CMOS battery is what I'd reach for.

My wild guess is an issue with having two loaders on that system. I think it is saying that one drive has one version of a loader and the dvd has another.

Can usually get to boot from grub command line, see if it has find (or is it locate?)