I cannot connect to mobile broadband network

гm using Ubuntu gnome 14.04.3. Today all of в sudden I cannot connect to my М Broadband network. it is displayed in the nm приложение but when I click on it says connecting and the it says 'off'. I tried several укради. I unplugged and then again plugged the модем in my computer but with не result. I restated my computer several укради. не result. I even deleted the поля in /etc/NetworkManager/system-connection.

Then again created new connection but не result. I only remember adding these lines:

IPv6
net.ipv6.conf.all.disable_ipv6 = 1
net.ipv6.conf.default.disable_ipv6 = 1
net.ipv6.conf.lo.disable_ipv6 = 1

to /etc/sysctl.conf

After watching this видео

https://www.youtube.com/watch?v=RqBjkSqSmBo`

(the first line I actually typed '#' without the coutes. I cannot write it ватт / или the quotes here)

How хан I connect to the network using GUI?