Hi staplesguy,
I have already responded to the support ticket you had submitted, but I felt I should leave a response here as well.
The first thing I would suggest is that you should attempt to restore the Multipurpose USB Device. If any of the files have become corrupted, then the DOS environment will be unable to load correctly.
To try and restore the USB Device, follow these steps:
1) From within Windows on a known good PC, insert the Multipurpose USB Device into an available USB port.
2) Insert the PC-Doctor Service Center Diagnostics CD and wait for the autorun menu to appear. Note: If you have the optical drive's autorun feature disabled, you will need to browse to the Diagnostics CD and launch Setup.exe.
3) From the menu, click on the option "More -- advanced options" and then select "Multipurpose USB Device Restore Tool" to reset the USB key to its original state.
I also wanted to mention that Service Center 7.5 DOS is not UEFI compatible. In order to use 7.5 on a UEFI system, you must first disable Secure Boot and enable Legacy Boot Mode (the names may be slightly different and configurations may vary).
Please let me know if you are able to resolve the issue, or if you have any other questions.
Thanks,
Kris