Inspiron 6400 Keyboard stops working!!!

I have Inspiron 6400. All of a sudden my keyboard stopped working, then it will work again, then stop, then work. Also, the media control buttons on the front quits working at same times that the keyboard quits working. I have disconnected & re-connected the keyboard & same problem. Anyone have any ideas what may be wrong? if I use a usb keyboard, it works, but every once in a while, I will have to hit the "alt" key to make it work. Please help!

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