AirPort doesn't find any networks I have a 13'' MacBook Pro from early 2011. Suddenly it can't find any WiFi Networks anymore. It used to find networks (including mine) at my home, but now it doesn't.

I cant remember when this happened, most of the time i'm using ethernet.

I installed all updates, repaired the permissions, tried do de/activate Airport, deleted

 /Library/Preferences/SystemConfiguration/com.apple.airport.preferences.plist
 /Library/Preferences/SystemConfiguration/NetworkInterfaces.plist
 /Library/Preferences/SystemConfiguration/com.apple.network.identification.plist


rebootet several times. Still no wifi.

Any ideas?
If your Mac is capable of running internet recovery, I would boot to the Recovery HD or full on internet recovery to see if the OS is the culprit.

If you can't join any networks from recovery HD it's very likely a hardware or severe interference issue is at play. At that point, you could take your Mac to one or two different networks that are known to work with Macs and test.

Being able to isolate the major systems helps when it's hard to guess what is happening.