If you are using the USB socket to apply power to the unit, firstly ensure you are using the supplied USB cable (TTV1AM20MB31) as it is needed to deal with the increased power requirements of the unit.
The unit also requires a minimum voltage of 5 V from a dedicated power supply (such as a power bank or mains supply) to function correctly. If the USB connection is not supplying enough voltage to the unit, the screen will display a 'USB power may not be adequate' message.
Pressing any button will restart the unit without the inbuilt NTRIP modem correction facility, however you will still be able to update the firmware of the unit and perform logging without NTRIP corrections.
Using the supplied RLCAB010H cable from the 3-way hirose connector on the bottom of the unit to a vehicle's 12 V cigar power socket instead of the USB for power will rectify this problem and restore full functionality, however if this is not possible, please change the USB power supply method.
If you are still having issues with the VBOX Sigma power requirements, please contact Racelogic Support.