iPhones recognized by computer but not by iTunes

Before updating to the latest version of iTunes everything worked fine, but now not one, but TWO iPhones in our house aren't found by the program. One is the first generation (received new in Oct. 2010) and the other is a 3G. We have windows XP Home, and I have tried ALL of the Apple Support guides. We are really at a stand still because you can't update, backup or download anything by computer and its getting really frustrating. I see that a lot of people are having this problem with multiple devices but my iPod syncs, just not the phones. Someone PLEASE HELP!!!