Two scenarios here, you either have had a handle failure OR an espag rod failure
Handles, sometimes the spindle comes loose and slides out of the handle itself causing the handle to just spin and not operate the mechanism at all
Espags, a common problem with espags is gearbox failure, if at some point the handle was stiff to operate when opening or closing this then puts undue pressure on the internals.
Ways to check....
Take handle off and look at the square bit in the mechanism where the handle spindle fits in to, is it still in one piece, these normally break apart because they are brittle, if its broken it may have fallen away and the square spindle does nothing now.......new mechanism required.
If its still there then get a good hold of the mushrooms or cams, (the bits that slide up and down to lock the window) and slide them manually, do they all move equally and in sync, does the handle move if its still on???
If not theres an internal failure within the gearbox, probably in the rack and pinion area......again a new espag rod will be required