Admob interstitial ad won't display

You should wait for the ad to be loaded. Only then, you can call displayInterstial() method, which would show the ad.

You can register for a listener, that will let you know when the loading is done.

interstitial.setAdListener(new AdListener(){
          public void onAdLoaded(){
               displayInterstitial();
          }
});

this did it for me.

// Begin listening to interstitial & show ads.
interstitial.setAdListener(new AdListener(){
     public void onAdLoaded(){
          interstitial.show();
     }
});

i still wonder why all the guys at google upload code implementing directions that just don't work after one follows them to the dot..

I had the same problem. The issue was that admob activity was not defined in manifest. Please make sure you have folllowing activity tag in your manifest file

<activity
        android:name="com.google.android.gms.ads.AdActivity"
        android:configChanges="keyboard|keyboardHidden|orientation|screenLayout|uiMode|screenSize|smallestScreenSize"
        android:theme="@android:style/Theme.Translucent" />