GM-GMC: Unable to engage 4 wheel drive for my 2002 GMC Envoy, gmc envoy, rear wheels

Question
I just recently replaced the battery for my 2002 GMC Envoy and now, with a ton of snow in Seattle,  my 4 wheel drive won't engage...I thought it might be a fuse...But then I thought it could be from the installation of a new battery...Could that happen? or is it just coincidence?...Help! My rear wheels are just spinning in this snow...Thanks

Answer
It never hurts to check your fuses first.  That being said...
It sounds to me like your TCCM, transfer case control module, has gone brain dead.  I have seen this on occaision, usually after a customer leaves a light on or something like that which results in totally draining the batter.  Unfortunately there is likely nothing you can do other than take it to a dealer and have the system reprogrammed/diagnosed.  
Hope this helps