You should be able to solve it this way:
1) Log in as administrator
2) Open an Explorer window and go to Tools -> Folder Options -> View -> uncheck "Use simple file sharing". (this will enable the Securuty tab in the file/folder properties)
3) Right-click on the file, or better yet, the folder where you store all your video files.
4) In the right-click menu click on Properties
5) Go to the Security tab and click on Advanced.
6) Go to the Owner tab and change the owner to the Administrators group. Also enable the checkbox "Replace owner on subcontainers and objects". Press OK.
7) Back in the Security tab, select the Users group. Set Full Control to Allow. Press OK.
8) Done! Now permissions are set properly and normal users can access the files again.
A full tutorial can be found here if needed:http://support.microsoft.com/kb/308419#4