Hi Adam,
I know what the root problem on your side now, it should be the PC driver problem, you board may not install the driver successfully.
Now, use the rev B board from mouser.
Please don't modify your newest board, find two win7 system PC, then follow me to test it now.
1. Install the P&E driver in your two win7 system
http://www.pemicro.com/downloads/download_file.cfm?download_id=53
2. Check J107, make sure it is in 2,3.
3. Plug the USB cable, can you find something is installing? This install need time, note, need time, you need to wait.

4. After the install is successfully, check the device management, please also give me your device management picture, this is my picture:


Please check it right now.
I have checked again on my side, if the PC driver is not installed for the new board, it will have the same issue as you.
Actually, the K20 work need the PC USB install the driver successfully, otherwise, both K20 and KEA128 won't work in the FRDM-KEA128 board.
Please check it.
Have a great day,
Kerry
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