Unable to connect to WiFi with my phone, how do I fix this?

About a week or two ago I had problems with my WiFi non of my laptops could of connect to it but after a week the problem was resolved, it was a DNS problem.

But now my Nokia N97 can NOT connect to the wifi, it connect but when I got to any webpage it would say “Invalid Server Name”. Now how can I fix this problem?

I really really want to use my phone connected to the WiFi because it’s so much easier than the phone network and I can see YouTube videos when I’m on the phone, when I’m on the phone network and watch YouTube vids I have to pay so that’s a down side.
And now my MSN Messenger on the phone won’t connect either.

So how do I resolve this problem?