need help with 4wd

i own a 1998 4wd envoy and i had it on blocks with the wheels off and when i put it into 4hi and 4lo the axle wouldn't spin but the drive shaft was spinning can anyone help with this problem or if u need anymore information about the problem let me noe???

Welcome to AF, this should be in the Jmmy forum as this is for the 2002 up Envoys, anyway the ft axles will not engage this way, they will just frre wheel until some slight load is put on them lock the axles.