Before submitting your question to support, please include a little background information so we can better understand the issue:
If you're trying to upload a video file, please tell us about it. What kind of file is it? How large is the file? An MOV, MP4 and AVI file under 100MB is acceptable.
Are you running Windows, OS X or Linux, and what version of that operating system?
How do you connect to the Internet? What is the speed of your connection (you can check at speedtest.net)?
What web browser are you using and what version (IE, Firefox, Safari, etc.)?
Do you have anything disabled in your browser, such as JavaScript or cookies?
Are you running any kind of Internet security software? If so, what is it?
Also, please describe your problem in detail so we can understand exactly what happened. Walk us through each step as you encountered the problem. This will give us a clearer picture of the issue.