Group window gone

[Kennin]

Hi there.
All of the sudden, I can't manage to find my group window anymore.
Today I was grouped, yet I couldn't find the box of the others.
Of course I tried [alt] + [g] several times, to no avail. Then I looked into my options menu, and the shortcut IS still [alt] + [g], so that's not it either.

Anyone any ideas?
Thank you!