Print Screen key stopped working [duplicate]

I use Windows 7 SP1 x64 Ultimate and the Print Screen key stopped working: no image is put in the keyboard when I hit Print Key. Nothing happen when I hit Alt + Print Key either.

The issue affects the two keyboards that are connected to the computer. Windows' snipping tool works fine. Copy-pasting text works fine too.

I haven't tried to restart the computer, my guess is that it will work then, but I am curious to know what could cause the issue.

Solution 1:

After killing my processes one by one, it turned out that Dropbox was causing the issue.

It might be due to the fact that automatically saved in my Dropbox account but it's the first time the issue occurs since I started using this option one month ago.