A little while ago, my Debian sid system stopped mounting CDs. Shortly thereafter it stopped mounting USB devices also. After searching around a bit I found a solution here (the problem was with Consolekit): https://lists.debian.org/debian-user/2011/10/msg01252.html
The solution is to create a file
etc/polkit-1/localauthority/50-local.d/consolekit.pkla with the contents:
Identity=unix-user:your username here
of course replacing your username here. Also create
/etc/polkit-1/localauthority/50-local.d/udisks.pkla with the contents:
Hope this helps if you run into the same issue.