Mac book halv keyboard stops function
m,l,k,j,p,o,i,u,9,8,7 do not active.
MacBook Air, Mac OS X (10.7.5)
I'm not sure how much you could do about this yourself. It could be caused by crumbs or liquid if you tend to eat near your computer or have spilled liquid into the keyboard, or the keyboard could simply be wearing out.
Also not clear on what computer you have. You posted in the MacBook category, but mentioned a MacBook Air below your post.
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If you're not comfortable with DIY repairs, you could find out how much Apple or a third-party reseller would charge to repair the keyboard for you.
<Edited by Host>