2000 Chevy S-10 Won't go into four wheel drive.

Other Category problem
2000 Chevy S-10 V6 Four Wheel Drive Automatic 65000 miles

When I try to put my 2000 s-10 into four wheel drive using the electronic push button control, the 4hi and 4low lights blink for a few seconds and then go back to 2hi which has a solid light. Any Ideas as to what is wrong?

Thanks

Roantech1