I too had trouble with my wireless connection - it looked as if, on the desktop that the USB adapter had given up the ghost. Having pulled practically all of my remaining hair out <g> I finally uninstalled all the software that BT gave me and tghern reinstalled it afresh. Once I had typed my WEP details in all was OK - repeated it on the other desktop and then that was OK too. The laptop in this case just reponed to the 'Connect to'. It's surprising how many times a reinstall works.
Have you a Restore Point before the day the trouble began? If so, try that. It can be very frustrating as I found out - I stopped short (but only just!) of kicking them through the window!!