I cannot upload files to my "flashed" Galaxy S4 topic

I have a Galaxy S4 that is flashed to Verizon Prepaid (originally U.S Cellular) I am trying to send pictures and files, like songs to and from my computer, but when I plug my phone into the laptop I hear a "bing" but nothing comes up. On previous smarthphones I've had, on the phone it would give me options to use as a disk drive ( where I could upload or download files to my phone) But I am not getting anything. I am new to the Galaxy series so I am not sure if its a setting or if its because its a flashed phone.
Also I was trying to use the Samsung Kies, but (after I installed the program) I'd plug my phone into the laptop but it would say device not supported. I am guessing because it's flashed ( it doesn't recognize it as a Galaxy S4 ) Will the Samsung Kies not work on a Flashed phone?

Thanks
jake