The clipboard may be corrupted, or disabled. When you copy something it copys it to the Clipboard so that you can paste it later. check to see that the Clipboard service is enabled. go to START , RUN, Type Services.msc. Look for clipboard and make sure its automatic, and enabled, and started. If it is. then you may need to try something else.
Jakou máš klávesnici? S vlastním driverem nebo generický od M$?
Jakpak v tom nouzovém režimu? Copy&Paste funguje?
A nepoužíváš náhodou Putty nebo Remote Desktop?