Hey, Rangerix! Have you tried the suggestions on this thread? The different region link usually works for the installer issue.
As for when battle.net is opened, is the network error when it tries to install a game? If the different region link does not work, could you include a WinMTR file using the IP Address/Host: us.patch.battle.net? Run the test until the problem occurs for 5 to 10 minutes. Copy and paste the text file created and paste it between two ~~~ like so:
~~~
WinMTR Here
~~~
If you have issues pasting here, use Pastebin and post the end of the link. (ie. 123456 for pastebin.com/123456)