Keyboard shortcut reset?

When command V doesn't work does the menu option work? I ask because sometimes when you copy something it doesn't get placed into the clipboard and it just seems like paste isn't working.

Do you have a keyboard shortcut program running (like Keyboard Maestro)? Did you recently open the Keyboard Preference Panel and change an application's shortcut? Does this problem affect all programs or just some (one)? Did you recently change a keyboard shortcut in the program that is causing trouble? I ask these questions because a shortcut like paste doesn't just get changed randomly. It is more likely that you unintentionally gave the CMD-V to another menu option without realizing it.

Open System Preferences and select the Keyboard tab. One of the options of the window pane to the left should be Application Shortcuts. Select it and see if command v is applied to another menu option for All Applications. If not and if you have no Keboard Macro program running I don't know how this happened now how to fix it.