I hate to hear you are having trouble with installing facebook to your device. You can remove the app from your device and do a soft reset but removing the battery. Once powered back on, dial *228 press send and select option 1 to re-program. If this does not resolve the issue, a hard reset would be recommended. Once the hard reset has been performed you can then go through the process of adding the facebook application.
From the home screen, select Applications.
Select Settings.
Select Privacy.
Select Factory data reset.
Select Reset phone.
If presented, enter the current passcode or draw the unlock pattern.
Select Erase everything.