Unable to connect to the internet and browse

Hi
I have a desktop computer that and i have recently had my tower cleaned back to factory settings and had windows XP installed as its what I am familiar with and now I cant connect to the internet. It is saying it's connected but everytime I try internet explorer it comes up with "cannot find server'. I have been on the phone to sky for 2 hours and they still don't know why. Every other device is working on wifi. I have tried going into control panel and following their instructions but nothing is working. PLEASE can someone help, i'm going stir crazy.
Thank you