4wd will not engage

What is your question?

I am having an issue with the 4wd engaging. I haven't used the 4wd since possibly the summertime. But, when I push the 4wd button the 4wd light just flashes and will not engage. I drove around for a while and tried again and it will still not engage. When I toggle the button on and off I can hear a click coming from the shifter, but I think that's normal. Could it be the winter is preventing this from engaging? I have never had this issue before. What, if any suggestions on this problem?