s104x4

My 2000 4 wheel drive S10 Blazer will not go into 4W high or 4W low. It has a 4.3 liter engine. Sometimes the light will flash on the 4W high button, most of the time it does not flash. The same happens with 4W low. I do hear a clicking in the box on passenger side door as if it is sending a signal when I press the buttons.My service engine light did not come on and I uused a code reader to find any problems and there were none.I have an electronic transfer case and 3 buttons on the dash next to the steering wheel:2whi,4whi,4wlow.It is too cold to get under the car and snowy and I have no garage.I do have a person capable of working on cars so if I can get some ideas of things to look for or at I would appreciate it.The number on my transfer case is NP235

Is the service engine soon light on? Is the service 4WD light on? If so, what codes are stored? Which transfer case do you have? On the rear of the case, toward the drivers side of the rear driveshaft, there is a metal tag that will tell what model transfer case it is. Different cases require different diagnostic and repair procedures.