Things to check:
- Does the upload work with a different browser?
- Does the file name contain any special characters (?, $, ', @, etc.)? If so, there may be a bug that prevents it from sending.
- Is the file too big? The limit is somewhere under 2.56GB. If the desired video is larger than that, try lowering its resolution.
- Open Video Editor (comes with Windows).
- Select New video project.
- Choose a name for the resized video.
- Click Add and select the file you want to shrink.
- Hit Place in storyboard.
- Select Finish video.
- Choose a lower quality than the recommended one.
- Export.
- Upload the new, smaller, file.