Ubuntu login error

Okay, I recently downloaded Ubuntu for my PC, to begin to replace the Microsoft XP OS I've been havng to put up with, but I've been having some issues I could use advice on. Whenever I try to login normally into Ubuntu it will play the login tune, then my screen will blank out and i end up back at the login screen a few seconds later. I've only ever been able to successfully log in using the "Failsafe GNOME" login setting, which I think may be a cause for my second problem, where my computer can't access the internet with the Wi-Fi connection I usually use, but only with a wired connection to the router. The WEP key is correct, but I can't access the internet without laying a cable between rooms. I don't have either of these problems when I start up XP, and I could really use some advice or tips on how to deal with this.