keyboard and trackpad not working

This was my first macbook air. I like it a lot, but I rarely use it. Well, I have a lot of computers at my house.

Since last year that I purchased the newer macbook air with the ssd, this was not doing anything much.Now this year with the ipad, even less.

However something strange happened to this macbook air when I took it out and try to sell it on ebay.

Let me explain. When I power on the laptop, right away, I hear the familiar apple boot sound. Then the laptop continue to boot. And finally

when it finish boot, I try to use it, the trackpad does not respond, so is the keyboard. I was thinking it may had crashed. But when I press

the power button. The shutting down message appear. So I know the computer did not crashed. I plug in a usb mouse and it worked. After

I turn it off and on a couple times. The keyboard and trackpad came back to life again. Then I put up the laptop. But the next day when

I tried it again. Samething happened. But eventually they work again.

Here is what I find out. If the trackpad or keyboard don't work, they don't work at the same time, never alone and since they are both usb,

they don't show up in system profiler. I tried press shift+control+option+power, the laptop turns off. So the keyboard maybe working.

I tried reinstall the system fresh, same thing. I will say one of 20 tried, the keyboard and trackpad will work. Maybe more, not too sure.

When it work, they appear in system profiler.

　any boady knows wich is the problem in my mac