My keyboard and error message

I plugged in my computer, which hasn't been turned on in 3 years...I got this message on the screen:

Windows could not be started because the following file is missing

/windows/system32/config/system

You can attempt to repair this file by starting windows setup using the original CD ROM

Select "r" at the first screen to repair

First of all I'm not sure what all of this means and secondly the keyboard is not responding so I can move the mouse (it is not showing up) or type anything in.

HELP