Cannot Access WRT-45G Router using Wireless

I have a problem with my Router, I cannot access my laptop and my PC in my router using wireless. When I used a cable, it connects to the internet but when I used wireless, I cannot access the internet. Here is the configuration:

Security mode: WPA-SharedKey
WPA Algorithms: TKIP

Please help. Thanks.

Are you using DHCP or static IP setup?
When on wifi, does your computer get an IP from the router.

Have you tried with WPA off, just to see if that is what is causing an issue.