I came across this same issue, my laptop is running Windows 7. This is what I did to mount the micro sd card...
1) After connecting your phone to PC, a USB notification will appear at the top of your screen. Drag the notifications screen down. Click on "USB connected" notification.
2) A new prompt will appear stating that you have connected your phone to computer via USB. Click the "Mount" button.
You have now mounted your micro sd card and should be able to access it through your PC. Hope this helps.