Password required to start LinuxCNC from USB stick

Assuming it is a desktop PC, those will always have a "Clear CMOS" jumper or a very small button on the mainboard.
Even removing the battery (2032 button type) for 10 to 15 minutes will reset the BIOS settings removing the password.
If it is a HDD password, none of the above will work, but changing the HDD will work.

The mainboard is a MS-7646.
It hould be this page of the manual:

Yup, that is it.
Move the jumper, leave it for 3 seconds, move it back to where it was.
Boot the PC.

It's not easy to access. I'll do that tomorrow.

Hi,
I think the problem is another one: this morning I have started the PC that I usually use and it asked for a password, in a window identically designed as on the other computer, whereas I have never been asked for a PWD.
I have removed the USB stick that was in the computer, but not bootable, and restarted. The computer didn't ask any more for a PWD.

So it seems not to come from the BIOS!

Do you use a stick that is protecting it's data. There are such ones. Try another stick

No, I don't, and I am not sure if the problem is the presence of the stick at the bootup.