Using Alt,Ctrl,Delete won’t come up

I have always used Alt, Ctrl, Delete to close all running programs so I can run defrag and scan disk. It no longer works. When I use those three keys nothing happens. Where did they go? I’m a novice at this so step by step will help. I have tried “regedit” it is there. No virus. Tried both sides of keyboard-nothing. I’m lost!! Even tried to go to safe mode to defrag but am lost without the mouse….