I apologize in advance for what I assume is a very silly question, but I just got this forum software and was able to rearrange blocks from the frontpage of the forum. I'm guessing I've changed something so I'm not able to do so anymore.. Where do I enable this? (I'm talking about the little arrow on the left side that brings out a menu)

Make sure logged in as admin.

Also addition to chilihead's info check this: https://community.invisionpower.com/topic/421510-no-sidebar-after-upgrade/?do=findComment&comment=2589545

I guess it was a permission problem. I added the user to the "moderator" secondary group and got it back. :-)