Monitor the kernel messages log when inserting a pen drive. Is it detected? Does it indicatate anything about mounting on your behalf?
sudo tail -f /var/log/messages
Then insert the pen drive.
Enter " polkit-auth --user <username>" in the terminal.
Does it list the policy:
Look at the PolicyKit configuration program. Does it allow mounting usb drives? You can use this program to allow mounting pendrives (mount-removable) if it isn't listed.
Besides policy, is the pendrive itself OK. If the filesystem is corrupt, you won't be able to mount it. Try to mount it manually to make sure it can be mounted.
Some pendrives are formatted without a primary partition. The entire device may be formatted as if it were a partition. E.G. suppose that the filesystem is on /dev/sdc instead of on /dev/sdc1. This may cause problems with auto-mounting.
Last edited by jschiwal; 04-16-2011 at 12:37 PM.