I have a MacBook Pro, 13-inch, Mid 2009 with OS X 10.9.5.
I suspect two things that might have caused the trouble:
Recently I had to replace the keyboard. After replacing the keyboard everything worked fine for a while.
I have also recently failed installing Windows with Bootcamp. The keyboard and trackpad worked before.
Now the keyboard and trackpad do not work at all. Though doing an SCM reset by using Shift Control Option and power keys seems to work as the macbook doesn't boot and I see the battery LED light up for a second or two (I'm using the Resetting the SMC on portables with a battery you should not remove on your own method). The power button works normally.
So the question is: Is it a hardware problem or a software problem? What should I do to make it work again? Is it worth it to do a clean system reinstall?
Update: System reinstall didn't help. I got back the keyboard backlight, but pressing the keys or using the trackpad still doesn't work.
Update #2: After one and a half years both the trackpad and the keyboard woke up of the coma and are working as if nothing has happened.