NHCLC,
If I understand you correctly the system is booting from the USB key but then can not lock?
The system BIOS is set to boot from a USB floppy?
That could be the issue the MUD does not emulate a floppy. If the BIOS is not set to boot from a USB Key, PCDR may not have access to the locking system.
There are a percentage of machines that will not lock to the MUD in DOS. This is because the BIOS does not fully enable the USB subsystem and relies on the Windows drivers to do so.
If you are unsuccessful we do have another option. Service center for legacy systems, it is a CD that does not rely on the USB key for locking, it uses the distribution media.
Please send me a PM with your phone number and we will get you fixed up one way or another.
-Fred