Hi Joey,
It is in Setting-Application-Development-USB debugging? Have to remove the usb cable from the phone first. I personally seldom use this for file transfer.

Alternatively, go Setting-Wireless and Network-USB utilities-Connect Storage to PC

or use KIES but slow, buggy and cranky. It works when it worked.

If transferring movie from one S2 to another S2, better to use Direct WiFi. Super super fast.
Setting-Wireless and Network-Wifi Direct settings. Just like bluetooth, needs to pair.
Read: http://androidadvices.com/galaxy-s2-wifi-d...-data-transfer/

Hope this can help and Enjoy the great weekend.