Can not connect to ROS core

I have been trying to connect to roscore, but when ever I try I get following error:

"cannot connect to ROS master at http://localhost:11311. Check the specified address or hostname."

I have done all the neccessary connections and everything to make it run, but still do not get why its happening.

[Aghamarsh Varanasi]

Did you try rosinit ?

[Faiza Gul]

Yes, still but the same error is generating.

[Xiaohu Li]

Did you solve it, I also encountered the same problem?