Try navigating to /Applications/System Preferences/Keyboard/Keyboard/Key Repeat Rate & Delay Until Repeat (in 10.6.8, anyhow) and try toggling and other fooling around with the settings...maybe restart afterwards.

Edit: You can try logging in to a test user account, but given the sporadic nature of your problem, it's liable to be a long journey.

Last edited by artie505; 08/22/15 02:09 AM.
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