Keyboard error

My computer keyboard is messed up. When I type Y, the letter which appears on the monitor is Z, vice versa. What's wrong? What cousing it?

Answer:
Have you ever changed the keyboard keys with software such as Key Transformation? This software can change any button of the keyboard whatever you like.

If you do, try to uninstall the software and restart to return to normal. But if from the MS-DOS you keyboard also messed up, there must be something wrong with your keyboard.