Unable to connect to secure wireless network Windows XP/Ubuntu 12.04

Hey there, I recently set up a wireless network. My friend in the same house running XP is able to connect using his laptop without difficulty with a less powerful signal.

The steps I've taken are these:

I've tried two operating systems (Ubuntu 12.04 and Windows XP) two different wireless adaptors (Dell M1530 internal adaptor and Alfa USB Adaptor which I get full bars on) and tried a different Dell M1530 laptop which I'm also having issues with. I've also tried to diagnose the network with a tool, but I'm totally unable to connect to it so I'm unable to get any more information. I'm regularly attempting to authenticate with WPA2, however I've also attempted with WPA and WEP.

If I try to connect to an unsecured network, it works perfectly. I'm totally stumped about this, due to the fact that I've used two different operating systems, two different adaptors and two different laptops (albeit the same brand). Any help would be very much appreciated at this point.