4x4 Problem

[ChevyKid1500]

Hello, I have a 1995 Chevy Cheyenne 4x4 truck, with a 305 5.0l V8 with a 5 speed transmission. I am having a problem with my four wheel drive. It has automatic hubs by the way. if i stop and put in 4 high, the lights wont come on show its in 4wd. if i put it in 4 low, the back locks in to the low gears, but the front ones will not pull. I have no idea of what it might be. any help would be greatly appreciated! ive tried everything shifting on the fly, backing up driving for a short distance to let the hubs lock in. it is so aggravating not to know what the problem is. Please help!! thank you so much in advance! ChevyKid1500 (Justin Roberts)