77 C-10 HELP No front wheel drive !!!

[Roger in Republic]

I need some help finding out why my front end is not working. The truck is a 77 C-10. 400 / 400 with an NV 203 X-fer case. The first time I tried to use the snow plow I noticed that I had no front drive. The hubs are engaged, the t-case seems to shift OK. The truck will move in 4 Hi , 2 Hi and 4 loc but there is no power to the front end. Could this be a broken chain in the case or could it be as simple as a bum shifter? I have not been able to get under the truck yet as it wont pull the hill to my garage door in the snow. I will have to pack the snow with my wife's truck. Any trouble shooting tips would be much appreciated.

Thanks. Roger

PS there are no strange noises or the sounds of anything that may have exploded.