Q. The Mac App Store isn't working. How to fix?
First you must have built-in Ethernet at 'en0'. So, you must install drivers for your Ethernet device. It is also possible if you have built-in WiFi at 'en0'. USB devices cannot be made to look built-in.
If you're using Chimera/Chameleon, make sure you have EthernetBuiltIn=Yes in your org.chameleon.Boot.plist.
If your Ethernet (or WiFi, in the case of no Ethernet) is not at 'en0', try resetting the network interfaces. To do that, go into SysPrefs->Network and remove all interfaces, Apply, then remove /Library/Preferences/SystemConfiguration/NetworkInterfaces.plist. Reboot, then add all your network interfaces back, starting with Ethernet.
If you have no supported Ethernet, and only USB WiFi, you can use NullEthernet: https://github.com/RehabMan/OS-X-Null-Ethernet
