Unable to type special characters since upgrading to Win10

[Timrath]

I'm unable to type all special characters that require the Alt key to be pressed. €, ², ³, μ, and most importantly, @, are no longer possible with a German keyboard layout. I tried German German and Austrian German, and both failed to produce those signs. Normally, the @ sign is produced by pressing Alt+q, but since upgrading to Windows 10, nothing happens when I press Alt+q (or any other combination of Alt+letter).
Only German keyboard layouts seem to be affected, as I'm able to use Alt+letter combinations in other languages; just not in German.

 

[Timrath]

Update: This is now fixed, but I don't know how it fixed itself. All I did was to go into Control Panel, click on Keyboard, and check to see what drivers were installed. I didn't change anything, but the problem disappeared nonetheless.