Hi bandrewsays, and welcome on this board.
Sorry you're encountering such issue.
When plugging the unit with USB Cable only, are you sure you plugged the thicker part of the double-usb cable?
Thicker part carries power + data, thinner part only carries extra power.
Please also note that the unit won't be recognized if you plug DC power + the thinner part of the usb cable only.
If you still have recognition issues, it can be good to perform a factory reset of your unit, as TerryM said ( Hi Terry! Thanks !
)
you have to hold Main Cue selector + Mono buttons while powering up the unit with Dc connection only ( the 2 first buttons under the big main output knob)
Hope this helps,
looking forward to read you,
best,