Help with LG GD900 Crystal! :(

Hi guys
Im having problems connecting my LG Crystal phone to the computer!
When i connect the USB to the computer, Im prompted to choose the USB connectivity mode. However, when I click on a selection ( For eg 'Mass Storage') Im immediately brought back to the phone's Homescreen and not the screen that says 'Syncing/Connecting' !
The computer is also unable to detect the phone at all!
I've tried restarting but it isn't working!
Help!
Thanks guys

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for mass storage do you have your micro sd card in? ...