Go to Apple Logo > Systems Prefs > Keyboard > Click on Show Keyboard in Menu bar > Go to menu bar > Show keyboard.
Then press the key that concerns you (for my iMac that is V). If the key you've pressed is highlighted in the keyboard viewer ... then it is working properly ... and the fault is elsewhere.
Significantly, this key is the one that enables you to test for software problems by pressing cmd / V. Read the document below.
Mac OS X: How to start up in single-user or verbose mode and check it out from there.
Copy does work but the missing letter in hae(between c and b on the keyboard) does the same thing.