Why can't my computer find my router?

Basically my computer can't find my router and my router is a Westell - Model 7500. I can connect to my Wi-Fi on my iPhone but not my computer. Anybody know how to fix this?

Hard to say from the given information.

Does your computer have a Wi-Fi network adapter?
Is it enabled, with the proper drivers?
Can you connect via Ethernet cable?

Beside those suggestion, maybe you can check your wireless security whether it is using WEP, WPA / WPA2, if your router using WPA / WPA2 security, can your try to change it to WEP, because for windows XP needs Service pack 3 in order to connect to WPA / WPA2 ( except if your windows is already using win 7 or higher)

and the other option is have your try to reset your router and try to re-configure again,

Hope this can solve your problem

From the information you are giving it is hard to say.
I would suggest you make sure the external Wi-Fi switch on your computer is turned on.
When you click on the Wi-Fi signal on your computer and I assume you have one does it display your network name or not. If it displays the networks name then your router is probably doing its job. Then Check all the settings on your computer and make sure the are correct. When did this problem occur and was it OK before that.
If you check the above and then come back with the info I asked I might be able to help more.