Also try if in the eclipse paths there is some duplicated
Luna - http://download.eclipse.org/releases/luna
Luna - http://download.eclipse.org/releases/luna/1234567...
Try both of them, one may work.
In my case, with 2 eclispes installed, in one of them the path
Luna - http://download.eclipse.org/releases/luna
works, in the other one, i must select:
Luna - http://download.eclipse.org/releases/luna/123456...
In both the internal browser can access to internet. Both are Luna (but one is RCM, the other one i don't remember).