Have you tried the following:
- Vox powered OFF. THis is IMPORTANT... Not in sleep mode but powered off
- Hold down the + side of the volume switch on side
- Press the Power switch while continuing to hold the + volume switch
- Release Power; unit starts to power up
- When a message appears abour a reset; release the volume switch
Those were the steps I followed for my wife's Vox yesterday. After that I had NO issues doing the upgrade to current firmware levels.