I have this problem, I'm trying to connect with a Windows XP laptop (Dell Inspiron) to the internet. We recently got AT&T U-Verse and all of our other computers can connect fine, it's only this one that has the problem. Now, what keeps happening is that I will go to the network selection screen and click on my home network. I enter the passkey correctly, and the laptop attempts to connect. It shows the message that it is trying to connect, and shows it for a long time (about 3-5 mins). It then simply drops the message and reverts to the network selection screen. No error message or anything.
Dell Inspiron laptop with Windows XP
Uses Linksys 802.11g network card
U-Verse uses Motorola NVG510
Problem: Just keeps reverting back to network selection screen while trying to connect.
Note: I had to actually faced the same old problem back when we switched to a different router and network, I had to go fix something in the registry, but I forgot, it was so long ago I had to do that.