Does it have an annoying BLACK square in your windows?
if yes:
Apple > System Preferences > Universal access
check if Voiceover is on, check it off.
check maybe if Mouse keys(under mouse menu), and Slow keys(under keyboard menu) are checked On, check them off.
(mine is in spanish, hope it's similar to your menu)
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One of God's own prototypes. Some kind of high powered mutant never even considered for mass production. Too weird to live, and too rare to die.