Okay so this is a bug that I've seen in both CS5 and CS6 - at different computers (different work computers, home computers, you name it). And if I recall I've even seen it in much older versions of Photoshop. I work as a 3D artist so I use Photoshop every single day at work so I'm in no way a beginner or "new user" of this software.
Symptom: Cut and Copy commands stop working COMPLETELY. Neither the hotkey commands (Ctrl+C, Ctrl+X nor the toolbar command works).
How to replicate: Select pixels either outside or at the image border via "Select all" or the "Color range" commands.
Workaround: Spam enter till it works, switch between tools, switch layer selections - Sometimes some of these work, sometimes not. Sometimes you can go back in history and repeat the command to get the copy/cut functionality back. Best thing though is to just NEVER USE "SELECT ALL" and to deselect edge pixels after performing "Color range".
Possible cause: When performing "Select all" or "Color range", some text field or other tool gets activated (although not visible on screen) which disables the copy/cut functionality - and the only way to get "out" of it is to do the above stuff.
Frequency: Bug appears and disappears totally at random. I've found that this bug mostly appears when I open a new image, perform Select all and try and copy it into another picture. Possible memory issue?
Priority: Orange - Needs to be looked into ASAP.