Unable to Unlock Users, or do anything that requires permissions

I’m have a Chromebook and I wanted to be able to download things onto it, so I got Ubuntu Linux version 14.04 using Crouton. Everything seemed fine and dandy, until I tried to plug in a USB drive. The message that popped up said “Unable to mount 32 GB Volume. Not authorized to perform operation.” I then tried to access some of the folders and got similar messages. After searching the internet, I found the unlock button which should work, but when I hover over it with my mouse, it says “System Policy prevents changes. Contact your system administrator.” I never saw anything about a system policy and I can’t find anything about it. I’ve tried to download programs through trusty and it doesn’t work. At this point, I’ve conpletely uninstalled and reinstalled Ubuntu and I still have the problem. I have no idea what’s going on and I can’t find any answers myself. Can someone please help?