Unlock Screen with ADB Android 4.2
If you are on 4.2.2, you might want to read e.g. ADB Whitelist As of the Android 4.2.2: Starting with this Android version, "remote devices" (i.e. those you run ADB commands from) must be authorized by the Android device (i.e. the one those commands are runnin on) -- so your Android device can tell "trusted callers" from "malicious attackers". You can also find this in detail on this article on AndroidPolice:


  The way it works is pretty simple - when you connect your PC to your Android device via USB, Android gets your PC's RSA key (an identifier token). In Android 4.2.2, when you have USB debugging enabled, this now causes a prompt to appear on connection, seen below.



(image source: AndroidPolice)

Update from the comments below:

Additionally, as Shurane pointed out, behavior of adb keyevent seems to have changed with Android 4.2.2: while before adb keyevent 26 was a dedicated "screen-off", and adb shell input keyevent 82 a dedicated "screen-on" switch, now adb keyevent 26 is a toggle which turns the screen off (when it's on) and on (when it's off), as noted by Pepelac.