Alt and alt gr keys stopped working on my laptop. They DO work with my desktop keyboard plugged in, the laptop Alt keys still don't work but the desktop keyboard ones do. I don't think it's physical damage because then it wouldn't be both Alt and Alt GR. Obviously something software related, but what?
It could be a driver issue... Have you recently updated any drivers?
Also, I can get more in depth if I know what this is in regards to as far as OS. And who makes your laptop? o.O
My HP Laptop has an Alt key on the left side of the spacebar and an Alt key on the right, but no Alt GR...
It's an Asus N53SN
Sorry about bumping this old thread. I am having the same issue exactly. It is only the Alt and Alt Gr keys. Both stopped at the same time one day. On screen keyboard Alt keys work. When using a USB keyboard I can use the Alt keys.