Ctrl+Shift in most cases (for me atleast), if that doesn't work go to your keyboard's language settings and you'll probably have to switch it back manually then.
I have the same you need to do something with Ctrl, so just hold control and start smacking some shit.
And each time you check if it works, that's how i fix it most of the time.
Thats where you should have posted this.
Well first you need to tell us what type of keyboard it is. Is it wireless, customizable, or anything like that?