The underlying connection was closed: An unexpected error occurred on a send.
I followed every single sugestion to solve this, but this error was persistent.
You know what was it?
I changed my internet provider last month, and I experienced some troubles to get a good connection, despite the high download rates. I returned to my previous internet provider, connected to the VPN of my job, set Firefox as my default browser (I was using Edge), delete the user data with the command "./devenv.exe /resetuserdata" (devenv.exe is in "C:\Program Files (x86)\Microsoft Visual Studio 12.0\Common7\IDE") and I activated the localization system in Windows. Finally the login window showed up, VS 2013 openned and asked me to uptade the license and it was done.
I lost 3 days of work because of this. I hope you don't need to.