My 4WD button lites up but the front wheels are not engaged

What is your question?

I have been having problems with the "service 4wd" for the last 2 years, after cleaning connectors , I thought the problem may be over, every once and a while the service lite comes on, I reset it , test it , everything changes (lites), I hear it change to low 4wd, but today, it snowed , I changed it to 4wd auto, 4wd, and the lights came on, and then I realized that the front wheels did not respond and drive. I was slipping as it was in 2wd. Any suggestions ? Don