How to re-activate my Command Shift 4 (for screen captures) I need to re-activate my Command+Shift+4 (for screen captures). I somehow lost this ability on my MacBook Air.

How can I do it?
Open System preferences App then go to Keyboard -> Abbreviations -> In the left panel click Snapshots  "scissor icon" -> Activate abbreviations.

and also...

Open System preferences App then go to Keyboard -> Keyboard Shortcuts -> In the left panel click screen shots -> select options on right frame.