2000 silverado 4x4 not working

I have a 2000 chevy silverado and the four wheel drive isnt working. I jacked it up put it in any of the 4wheel drive selections, auto/hi/low. The front wheels will spin until I put my foot against them, and they'll stop. With the engine shut off I got under the truck while my brother spun the front tires and I couldn't hold the front driveshaft from spinning. This makes me think the actuator on the front drive is good. Oh when I put my foot against the front tires to stop them the front driveshaft stopped spinning. Everything sounds like it is working, but isn't, so I replaced the transfer case motor, had to be it. Wrong, it still isn't working. At first any of the lights on the push buttons would light up like it is in four wheel drive, now after the new transfer case motor it will go into all but 4hi, just blinks and goes back into the previous gear. I think it is because it has a code in it, although I haven't had it to the shop yet. Any one please help