PC Won't Lock

My PC won't lock no matter what way I try to do it.
Via win+L, ctrl+alt+del or the start menu.
When I press one of these nothing happens at all.
Any ideas?!

Hi, To confirm there is no malware involved, please scan your computer with malwarebytes anti-malware. Follow the guide here: How to use Malwarebytes' Anti-Malware to scan and remove malware from your computer.

Also, please run the SFC file checker (the sfc /scannow command) 3 times and post the last log file here once you have completed it for me. Follow the directions here: SFC /SCANNOW Command - System File Checker


Stephen