Transfer case wont shift out of 4hi

I have a 2001 chevy suburban 1500 4wd. The service 4wd light has been coming on intermitently but today put it in 4hi and I cant shift back to 2wd the light flashes and I hear the 2 actuators buzz and then it goes back to 4hi. I tapped on them and its the same also checked 4wd fuse its ok. Ialso pulled front axel acuator out to see if it was stuck seemed ok cant get top screew out of acuator on transfer case. What do I do next? Thanks