I've been using a Microsoft-made external (ergonomic/split) keyboard, connected via USB, to my Mac laptop without a problem for years. My OS is 10.6.8. Out of the blue, random keys stopped working on the keyboard: Shift + any of the numeric row of keys do not work (for example, can't use Shift + 8 or Shift + 9 to make open/close parenthesis). The backspace key is not working and several other random keys, while other ones do work. The keyboard that's on the laptop works fine; it's only the external keyboard that is affected. The only unusual thing I did recently was use an external USB stick to load some files on my computer. No new software was installed.
I googled this repeatedly and found similar descriptions of issues, but none of the proposed solutions worked:
I tried deleting the keyboard layout as follows: rm /Library/Preferences/com.apple.keyboardtype.plist
and then replugging the keyboard in. It prompted the keyboard setup wizard which asked me to identify key to the right of Shift on the left side of keyboard. When I pressed that key, it recognized it. It then asked me to press the key to the left side of Shift on right side of the keyboard. When I pressed that key, it didn't recognize it and then it said it cannot identify keyboard.
I tried looking at various settings in System Preferences -> Universal Access/Keyboard shortcuts and could not find anything unusual.
Any idea what is causing this and how it can be fixed? It renders the external keyboard totally unusable. Again, I've been using this keyboard with this computer for years with no issue! Other external devices like my wireless mouse (connected by USB as well) work fine.