Can't upload mp4 files

I downloaded 4.3.1, but I don’t know if it’s running or not. I already read two or three pages of forums but none address this. I know some of you are rolling your eyes and thinking, “Why didn’t she just..” I am just learning how to do this and I am old, so just imagine you were sent back to 1950 and told to teach a bunch of kids and communicate with their parents without any electronics. I’m trying to do the opposite.

The videos start to load and then stop. They are not long (most is 20 min) and run from 360-720p.

My site is flumw3kids.com