Is it external? Then try disconnecting it.
Looks like this could be a BIOS problem. Does it actually attempt to boot from the Mint USB?
If not, then you will need to enter the BIOS setup screen and change the boot device order. Put “USB HDD” at the top, “internal HDD” and “CD drive” in the middle, and anything else at the bottom.
This might get rid of the “boot from URL” you’re seeing, by demoting “PXE network boot” from the boot order.
Which errors are you getting? Because if it’s these ones…
then everything is OK. Those are perfectly normal boot messages.
If it’s the same errors, try the same solutions. If it’s different errors, tell us what they are.