Wifi connected but wont work iPhone

I have an iphone 4. I recently got internet back up at my home using an older wireless router. At first my wifi worked, but then we tried to hook up a older imac osx computer to the same router. After this my wifi just stopped working. Ive disconnected my cable modem and also the wireless router, and reset my network settings on my iphone. It still does not work. I know there is a problem if my ip address on my iphone starts with 169 BUT, my ip address nor the subnet mask, router or DNS shows information to know if i have this problem.
Overall, my iphone picks up the wireless, has a check next to the network, but the wifi signal on my homescreen doesnt display even though i have the check. It just still has the E
please help!
Inspiron 6000 Windows XP