Here's one way to investigate it if it's not automounting:
1. From a terminal, run dmesg
as root. Scroll the output of dmesg to see whether your computer is actually seeing the flash drive. If it is, the dmesg output will tell you how your computer is seeing the flash drive.
2. Add the flashdrive to your fstab and mount it like a regular drive.
Here's a longer description I wrote about this a long time ago when I was figuring out how to mount my podplayer.
It has a lot of links to explain what I just said.
I'm no expert. I just made my mistakes earlier than some other persons.