When I first got my S4 and connected it to my computer to transfer files, it worked like a charm. Now, I continually get the following error:

I've tried on two different computers and get the same error.
I've tried three different USB cables (all Samsung) and get the same error.
I've tried changing from MTP to PTP connection and I still can't see the files on the phone.
The Verizon Software Upgrade Assistant loaded fine and sees the phone when it's connected.
I downloaded Kies and have tried connecting via USB cable and nothing happens. It just says "Connecting" for hours on end.
When I tried to connect via WiFi, nothing happened, either. I input the code on the phone on the computer, and nothing.
What gives? How can I easily transfer videos from my computer to my phone? It shouldn't be this difficult!
Thanks.