Keyboard & Trackpad not working :'(

2 days ago my macbook air keyboard and trackpad suddenly stopped working, the power button is the only button that works. But all function works fine with the external USB keyboard and mouse.

I read many posts here and tried to start up to Apple Hardware Test, reset PRAM, reset SMC and start up in Safe Mode, after each step it works for a few mintues but then fail again...

Finally I full reinstall the MAC OSX , but still doesn't work :(((

So it's the hareware problem? I have to go repair or buy a new one?

Anyone can help me?