Wow, I had this problem just this week! And just got access to my MicroSD...
Accessing your MicroSD
My MicroSD card works GREAT on my phone, but when I inserted it into my card reader and plugged it into the computer (Ubuntu 12.04), it didn't read! Well, this MicroSD card was a 16GB, Class 4 so I thought maybe it was due to the Class that it didn't work. Since, when I plug in a 2GB MicroSD, it works great! Works on my phone as well as using the card reader.
What I did:
Updated my USB drivers as well as my computer and it's all GREAT!
Here's the command that I used:
sudo update-usbids && sudo update-pciids
And then use the Software Center and just do a full system update. That's it.
The post where I got the info from: Ubuntu 10.04 USB drives not mounting! - These are instructions for Ubuntu 10.04 but it worked for my 12.04. *I didn't have anything to do with mount-manager at all.
Accessing your internal storage
This is something that I'm not an expert at but I'm quite sure it's what the rooting program using the ADB connection did to my Android when it needed to install the sudo binary.
But here's a link I hope will be of a great help to you - How to access intenal storage or internal memory of Android while conecting to PC?!