What LifeIsABeach said. Once you have plugged the phone in to the USB, there will appear a USB icon in the top status line on the phone. Swipe downwards to bring up the notifications. One of the notifications will say
Select to copy files to/from your computer."
Touch that notification with your finger, and a dialog will come up giving you the choice to "Mount" or "Don't mount." Choose "Mount."
This will make the phone media visible to the computer.
Once you are done, use your computer's commands to disconnect the drive. You should also use the *phone's* command to turn off USB storage. Do the same thing as before, swipe down to bring up the notifications and choose "Turn off storage."
It may take a few tries, it took mine a couple times to work. I also got a new computer with windows 7 and I have had a few issues with connectivity. And also the 64bit OS has been a pain with some compatibilities too.