Why can't I switch from 2 wheel drive into 4 wheel drive?

check under the vehicle to see if the selector is actually moving on selection
Take it in to an accredited service center to see what has seized up from non use

Call the dealer.

It could be a junk switch or it could be bad contacts inside the transfer case motor.. Does the transfer case switch to the selected gears? Everytime? If so, you might try another switch. If it does the same, I would say the motor contacts are bad. Replace the motor if you want the lights, But I personally wouldn't do it until the motor quit switching gears. They're not cheap.

Put it neutral and then hit the button for 4 Wheel drive. It should work then and do the same to take it off 4 wheel drive.

THEIR ARE ACUATORS ON THE FRONT PUMPKIN AND THE TRANSFER CASE THEY GO BAD ALSO THERE IS A MODULE UNDER DRIVER SIDE DASH,SQUARE BOX.IVE ALSO HAD TO REPLACE THE WIRE HARNESS THAT GOES TO THE FRONT PUMPKIN MODULE,ITS TRIAL AND ERROR.LUCKLY I BUY LOTS OF SILVERADOS AND YUKONS FROM SALVAGE AUCTIONS AND DO A LOT OF REBUILDING OF THESE TRUCKS.SO I HAVE PARTS.YOU REALLY NEED SOMEONE WITH A TEC 2 GM TOOL IN WILL BE ALOT EASIER.

Replace switch its bad.

usually the actuator will still make the light still come on if its bad I would check the actuator

problem with the switch on dash, light come on only but it will stay on 2 wheel

start truck leave in park press 2 wheel high button put truck in drive move truck,check for being in 2 wheel high, if still in 4 wheel low have switch and shift solenoid checked

I had that problem in my 1998 Blazer. There is a module on the passenger side of the truck, next to where the passenger right foot be. Remove the side kick panel to get to module. Disconnect battery before unpluging and pluging new mudule in. This unit controls the electronic switching between 2 and 4 wheel drive..Wes