Hmmm...
Would it be possible that the option to connect as a USB to the computer was reset?
So to make sure that it is on.
Go to "Settings"
Go to "Applications"
Go to "USB Settings"
*** Personally ***
I have mine to "Ask On Connection"
Mostly so that I know how the phone is being connected to my computer.
But that is a personal choice.
Hope that it does provide with some sort of solution.
Keep us updated if it does or doesn't work so that if not another option might be thought up.