If it looks like Windows is a bit hosed, and you're contemplating reinstallation: Assuming you have or will obtain installation media, try this before wiping completely:

http://www.pcworld.com/article/243190/how_to_repair_a_corrupt_windows_7_installation.html

If everything looks OK except network adapter(s) aren't working, it would be a good idea to check in the BIOS to make sure the adapter(s) haven't been disabled somehow. To access the BIOS you typically have to press a specific key during boot. You can also press Pause to pause the boot so you can read the screen, then Enter to resume boot process. Enabling/disabling network adapter will usually be in a section named "Integrated Peripherals" or similar.

>I am comparing all settings on this (my second computer, also Window 7) with the one I have a problem. In some online help I see that I need to click on "Change adapter settings" when in the Control Panel -> Network and Internet -> Network sharing Center. But on the "broken" computer, click on Change adapter settings shows empty screen :(
>
>>Are there any network adapters called avast or with avast in the name? If so remove them...
>>
>>>No, Use a Proxy Server is not checked. Thank you.
>>>And no yellow flags. All drives show to be Working Properly.
>>>
>>>>go to Start > Control Panel > Internet Options > Connections > LAN settings - make sure 'Use a proxy server' is not checked.
>>>>
>>>> Start > Control Panel > System > Device Manager - are there any flags showing?
>>>>
>>>>or maybe this? https://support.microsoft.com/en-us/kb/299357
>>>>
>>>>
>>>>>I go to the Device Manager and I see several Network Adapters. All seem to be functioning. Yet, I don't what to do next.
>>>>>
>>>>>When I run IPCONFIG I see message about all Adapters.. Media State - Disconnected. How to connect?
>>>>>
>>>>>
>>>>>>Hi,
>>>>>>
>>>>>>I unstalled Avast AV. But it took with the installation my internet connection. (I am typing this on another computer). How do I set up my Window 7 to be connected to my router again?
>>>>>>
>>>>>>TIA