Typical problem - Cannot connect to my own WiFi

Hi, I've just got my new iPhone back as my old one had a problem, everythings back to normal and synced up but it will not connect to my WiFi even though I know i'm putting in the right password. I never had this problem with the iPhone I sent back.

Its a 16GB legit iPhone 3G from o2 on version 2.2

Anyone know how to fix this, from what I've read its a pretty typical problem.

Cheers

 

Oh its fixed now, I just re set my router and that was it, it connected fine!

I've read so many comments about going into your router set up and turning off firewalls and all that *****, just re set my router and it worked so that was easy enough.