I have an issue with my old Photoshop CS ...hopefully someone can help me!

It works just fine, but some actions (Duplicate Layer, for instance) will lock the whole thing. Not bug and freeze, just make all options unclickable.
If I make that "forbidden move", all the drop down menus (file, image ... etc) will drop down, but every item will be grey (as if being unavailable ... can't click either), same for the X (close) at the top right. Only the Window menu will work fine, I can display/hide extra windows like Layers and Tools and whatnot. If I move over, the cursor will change (ie it's not frozen), but I just can't click anywhere.
My only way out is alt-ctrl-del

Any clue what's going on? Did I accidentally select some stupid option? Has my CS gone too old and has now retired? I'm stumped.

 

Is it only 'Duplicate layer' that makes it freeze?

 

I can use any tool in the Tool window, I can use most of the function in the Image menu (ie resize, levels, shadow/highlight ... etc etc), any Filter without a problem.

But Duplicate layer (either from the Layer menu or by right-clicking the layer) is the only one I've actually been able to pinpoint. Maybe other functions cause that problem, but thus far it seems to be the only one causing a problem ... which leads me to thinking I have selected inadvertently (sp?) some stupid option.

edit - funny enough, I can circumvent the issue (only identified it yesterday) with a copy/paste!