The wired aluminum keyboard on my in-laws iMac has four keys which are suddenly not functioning: Escape, the tilde key, Tab and Caps Lock. I tried trouble shooting it yesterday per the Apple support page (including booting into Single User Mode), to no avail. It is not anything inadvertent clicked or activated in Universal Access, nor am I simply not hitting the Caps Lock long enough to activate. I pulled up the Keyboard Viewer onscreen and when these keys are depressed, it did not show a corresponding depression on the screen keyboard. My guess is this is a hardware issue, which was my first instinct when I realized that the buttons are all grouped near each other, however if anyone has any additional troubleshooting suggestions, or similar experience, it would be much appreciated. Thanks.