Try clearing the cache for the Internet app.
Try copying the link first, then open the Internet app and paste.
Try a different Internet browser just in case the link doesn't work properly.
It is best to use WhatsApp or Skype for sending videos. Sending them over mms will result in quality loss. You can also use the link sharing option to share full quality videos.
If it shows the t-mobile logo when you power the phone on then I think it means the phone was (and maybe still is) locked on t-mobile.
Go to settings, about phone, status, sim card status.
What does it show there?