If it is an android phone, try this:
- exit any samsung software on the pc
- Go to Settings and enable USB debugging
- Leave settings screen (press home button)
- plug the USB cable to the PC and then to the phone
- press "Connect USB storage" under the pull down status/settings bar (or what ever you call it)
If it doesn't work, do the same as above with samsung pc suite opened on the pc.
Might help