1997 chevy blazer 4 high or 4 low will not engage

Hey guys- I have a 1997 chevy blazer that sat for two years while I put a reman engine in it.Now it is running again but when I go to select 4 high or 4 low with the electric push button dash switch it makes a real light sound as your driving like its trying to engage, but doesnt work at all. I considered draining oil and running dextron III in it for like 50 miles and draining. then new synthetic oil.Can any one tell me if there is something that may be a notorious problem with these transfer cases that can help me figure the problem out???? thanks