Originally Posted by squalliram
I have tried the WPA-PSK approach (AES encryption) and it does somehow make it work on my Xperia S (it did not connect to it instantly). Basically, there is an option of WPS (Wifi-Protection Setup) in my Xperia S which allowed me to do a Push Button Configuration (PBC) i.e. holding the router button for 3 seconds to allow my phone to access it. It assigned me an i/p address and thus made it work but spoiled it for my other housemates, so I had to get the setting back to WEP.I know it is more secure to use WPA, but I cannot change it without asking my landlord. Anyways, the point is that somehow my other phone connects to the router not instantly but via some route as given above. My question again is: Is it really not possible to connect it via WEP?
You are typing in a 10 character hexadecimal key right?(numbers 0-9, letters A-F) Not a pass phrase?
If you are 100% positive you are typing in the right key, you have to try another WEP secured network, if that works, then you know the problem lies with the router. Copy down then router settings and hard reset the router (usually a pin hole on the back of the router, press it for at least 10 seconds). If it doesn't work with another router, take the phone to a store and have them troubleshoot it.
However googling your issue, does bring up other users with the same problem when using WEP encryption, it's hard to say whether it is a Sony issue or just that the others are having issues with their router also.