If your revolver is an imported single action, you may have the base pin,(cylinder pin), pushed in too far.
All imported revolvers must have a hammer block safety installed and some of the importers met this requirement by designing a base pin that could be pushed back and locked against the hammer.
Pull the base pin out and see if there are two grooves near the end that sticks out from the front of the frame.
If you push the Base pin in and lock it on the first groove, the hammer should cock and the cylinder should rotate.
Pushing it in farther to engage the second groove will set the hammer block, a small portion of the base pin sticks out the back of the frame and engages in a hole or notch on the front side of the hammer preventing it from cocking.HTH