1999 Chevy Blazer no 4X4

Drive Train Axles Bearings problem
1999 Chevy Blazer 6 cyl Four Wheel Drive Automatic

my blazer wont stay in 4x4 it says service 4x4 when I push the button I was told by someone that looked @ it that everything up to the transfercase was working when I push the button u can hear it click in and back out from the glove box and some times it will go into 4x4 but then disengage itself after a couple blocks