Typing any keys on an external keyboard open apps. How to revert this?

I was typing like I always do using a USB keyboard with External Keyboard Helper Pro bought from Google Play. I usually type in Evernote. In a moment, I'm kind pressing more than one key a the same time - probably a Fn, Ctrl or Alt and other. I have no idea what I pressed. But since then, I *can't* type anything because the keys open other apps. If I press "e" in the keyboard, the e-mail on my tablet open, and if I press other key, other app open. I tried to figure it out, search in the settings from my tablet and in the settings of EKH, but I don't have any shortcuts configured. I'm thinking that I press some kind of shortcut that activated other shortcuts, but I don't know how to go back to what it's like before. How to fix/revert this?