Thread: Bricked Navman MY650LMMT

I've been looking for the same.

Try a hard reset. I don't know the exact procedure, I never dealt with this exact device before.
I found this:

while on charge, perform a hard reset to the device by poking the reset hole at the back of it. Hold it in for 5 seconds and the unit should reset to factory default.

Maybe this is not the exact method but you can experiment with holding the reset button alone, or both power and reset, or holding reset and then powering up the device, try while charging if it doesn't work try without. Try some combinations and good luck.