2002 chevy blazer 4wd not working

Ok here is what happen last winter my 4wd would not engage when it was cold out untill it got a little warmer I would push the buttons but the lights would just flash for a few minutes and then go back to 2hi. Now it won't engage at all lights just flash sometime stops and goes back to 2hi sometime they just keep flashing. also 4lo don't work or the 4wd auto. When I do push the buttons you can here the motor on the transfer case click one time, but nothing happens. If anybody can help me figure this out it would be great and save me alot of money.