I have an old S+W .22 LR Kit gun that my dad purchased back in the 1960s.  The gun is in good shape and shoots OK, but now I can't unlock the cylinder.  The cylinder rotates freely and I am able to dry fire the pistol fine - everything seems to work.  However, pressing forward on the thumb piece doesn't appear to do anything -- the lock at the bottom of the cylinder appears to still be engaged and the cylinder won't budge at all.

Any ideas?

The hammer must be down for the cylinder latch to unlock the DA pistol.

Dano523, the hammer is in the down position.

I had a S&W K-22  Model 17 of mine do the same thing.  It was REALLY dirty, so I took the grips off and doused it in carburetor cleaner and WD-40 paying special attention to the cylinder latch.

Worked the latch a few times and it opened.  There must have been some crud interfering with the forward/backward travel of the parts.

Hope you get it fixed, those old S&W .22s are the schiznitz!  I got my little sister a Model 34 just like yours when she graduated from high school, it is a 2" and she's carried it all over the country with her.  One heck of an accurate, beautiful revolver.

Arkansas_Rocketman, I'll try that.  To my knowledge, the grips have not been off this gun since the early 80s

I have one with the same problem.  The ejector rod works loose after a few cilinders of ammo.
What you have to do is tighten the ejector rod by hand and  the cylinder will loosen up enough to swing out.
Hope this helps.