'01 4x4 issue

Have a 2001 Tahoe...went to pull my boat out of the water yesterday and couldn't get the 4x4 to engage. When I push the button, I can here something try to actuate, but the light never stops blinking, and it never engages. No service 4x4 light, just the blinking indicator and no 4x4. Any suggestions on where to start trouble shooting this?

Thanks!
Craig