Will not engage in 4WD

I'm not mechanically inclined, so forgive me, but I like to have a vague idea of what I am dealing with when I take the truck in for service.

2004 Blazer
Problem: Will not go into 4WD at all anymore. First hint of trouble was the other day when I put it into 4WD. When I went to go back to 2WD it would not change. Pushed the button, but nothing changed, nothing flashed. I put in neutral while standing still and tried again. The 4-High and 4-Low indicators flashed and it went back to 2WD. Now I can't engage 4WD at all. If the vehicle is moving or in gear, nothing happens...no lights flashing, no clicking of switches. If I try while in neutral and standing still, the 4-high and 4-low indicators flash 2-3 times, then go out and it is still in 2WD.

Any ideas on what the problem might be based on this sketchy info? Any suggestions on things I can check to give a better idea of the problem?

I love this site, and when I had recurring problems with my old Jimmy, you folks put me on the right path in a day, I gave my mechanic the right info, and the problem was solved.

Thanks in advance,
Dave

What is the mileage?
Ever been serviced or repaired.
Fluid and fluid level good?
Is it the 236 transfer case with the auto 4W button.
Key on does all shift button lights coime on and go off for a bulb check and the indicate what gear it is in?

The 236 you need a transfer case/transmission case scanner to check it out and pull codes.
233 you ground pin 13 on diagnostic connector to get codes.

Check for codes and post back code no.

62,450 miles
Serviced as recommended by mechanic since I bought it (bought at 42,000).
No repairs needed since I have owned it.
Fluids good at last oil change, it is due soon, though, and I just checked the transmission fluid, which was where it should be.
No auto 4WD button. Just 3 buttons: 2High, 4High, 4Low.
I'll check on the bulb check after work.

I have no means to check the codes...I'll have to take her to the shop for that. Like I said, I'm no mechanic, I just am trying to get a handle on what I'm dealing with before I take it in.

Id no auto 4W button you can get codes by grounding pi 13 on the OBD11 connector and turning key on.
Read codes from shift button flashes.
Post back code no when you get them.

Thanks MT! I'll see if I can work that out tonight...it's all new to me. I really do appreciate the help!
Dave

You are welcome.
Let us know it goes.
Count the shift light blinks real close as the repeat the codes.