4x4 problem
 

In my 93 ranger the truck wont go into 4x4. When it would be real cold i would come out to the truck in the morning and start it and the 4x4 switch lights would be on and after truck would warm up the lights would go out. Ive tried replacing the push buttons several times and now i cant get the truck to go into 4x4 at all.. can anyone help me?????