4WD will not turn on

I have a 2002 S10. Ext. cab V6. When I go to put it in 4WD, the indicator light goes to 4HI or 4LO and it sounds like it engages but it doesn't. The light will say it's in 4WD and not blink. Any ideas?

It is either the 4wd switch or the motor for the transfer case.Do not attempt to repair the switch,buy a new one from the dealer doing it right the first time.