GU patrol not engaging 4WD

[ConnorSC]

G'day fellas, please forgive me if this is in the incorrect section, but I'm struggling to work out what's wrong with my 03 GU TD42 Coil cab. Drove up to Stockton on the weekend, dropped my tyre pressures to 12PSI, locked my hubs, and drove onto the sand only to become bogged instantly with no drive to the front wheels. The driveshaft from the transfer case spins when in 4wd, the 4wd light illuminates on the dash and the hubs don't make any grinding or funny noises. What could be my issue and how would I go about diagnosing? Cheers for any help

[the evil twin]

Had the vehicle long?
Been working in 4WD OK on tracks and rocks?
Auto or manual Hubs?
No diff lock fitted?

In 2WD with the vehicle on a hard surface...
Lock the front hubs, dive underneath and see if you can turn the front drive shaft by hand, the factory diff is open so if you can turn it something is busted.
Jack one front wheel each side alternatively with the other on the deck and try and turn the wheel, if the shaft turns that side is OK, if the shaft doesn't turn then that is the side with the issue

Always start with the simplest things and the easiest is to check the Hubs are OK, if it is factory open diff then a busted hub means no drive to either front wheel