You should ensure, to have GPS enabled on your device. Do do so:

1. Navigate to your HOME-Screen.
2. Press the MENU button on your device.
3. Select "Settings" from the menu.
4. Select "Security & location".
5. Check "Enable GPS satellites".
6. Go outside and wait for about 20-40 seconds while being i.e. on the AndNav's 'WhereAmI'-Screen and you should see a new icon in the status-bar of your G1 indicating that you have GPS activated, also there should be a small person-icon appear on the map, centering on your current location.
   
7. GPS is properly established when the Icon stopped Flashing !