I had the same problem, and solved it.
Problem: CTRL+C will not work.
Reason: On my computer, another program (Skype) was using Ctrl+C to answer calls. Removing the keyboard shortcut solved the problem.
Im assuming its a similar issue, maybe with another program in question. Try closing any program (even in the background) that may have custom shortcuts, IE, winamp, etc. You MAY have hit COPY to copy something, when the shortcuts were being set, or the program itself over-rides the general copy function. (explains why CTRL+X works) Creative wireless headset software uses CTRL C to answer calls, for example.
In a nutshell, reset all hotkeys on any open programs. Hope that helps.
