Use the steps documented in ... Connect Bionic to Windows 7 with USB Cable
My guess is that you need to set USB Mass Storage
and have it currently set to something else.
What you will see in Windows is two Drives ... one is the SD Card and the other is the SD-Ext card. Using Windows you can set the names to whatever makes sense to you. I chose BIONIC SD and BIONIC SD-E on my stock Bionic.
They were always assigned in the same order on my machine
8.00GB total = SD Card (not removable) (my rename BIONIC SD)
14.8GB total = SD-Ext Card (removable) (my rename BIONIC SD-E)