Did you use System Restore (SR) to the day before the problem?
SR does not touch our files so this is the first aid for such an issue. Beyond that, it gets technical, deep and can be upsetting.
My wife's Samsung notepad keyboard and touchpad have stopped working. The odd thing is that the keyboard does work at startup - I can press F4, arrows, Enter, etc to start up in safe mode, but still the keyboard and touchpad do not work as soon as we get to the login screen. I have tried system restore, unplugging the cord and battery. At the moment I can get it to work using a USB mouse and the on-screen keyboard, but would like to know how to fix the problem if possible. Any help would be greatly appreciated, thanks very much!