Stuck in 4 wheel high

I have a 98 blazer that is stuck in 4-hi. I had a problem in the past with it shifting into 4 wheel drive by itself but I could always shift it back. This time it shifted and will not go back to 2 wheel drive. I can push the button and the light on the button will flash and I can here the motor trying to shift the transfer case into 2 wheel but it will not go. I can shift between 4-HI and 4-LOW just fine. It sounds like maybe a transfer case problem but I am not sure where to start. Any suggestions. Please help.