List of targets in exlipse disappeared (( You can see the result in the image
And undefined error:
ANd 3:
In Eclipse go to Window -> Preferences -> Android and reset the sdk location
UPDATE:
It seems you have only updated the Android SDK version without updating the ADT. This can cause problems. Update the ADT to fix the problem. Go to Eclipse Help -> Check for Updates to update the ADT (Assuming you didn't install the ADT manually/offline)