Screen suddenly greyscale
 

As per title, my son's screen has suddenly gone greyscale.

• Tried restarting computer
• Tried another cable
• GFX drivers are up to date
• Have checked to make sure he hasnt accidently enabled windows colour filter

It was fine, he shut his PC down to get dinner and when it was turned back on this happened. Any ideas?

what monitor? did you go into the monitor settings to see if something was changed? Did you try the monitor on another computer or another monitor on the computer?