Kindly supply the model number of your access point and your router so we can guess the default IP address. My guess is that you have two seperate boxes, a router and a wireless access point. If they are from different manufacturers, it's likely that one is on 192.168.0.1 and the other is on 192.168.1.1. These are on different subnets and your PC will see one, or the other, but not both, unless you increase your netmask to 255.255.0.0. Use ping to check for connectivity before trying to access the web page configs.
You can find the gateway address of the router with: Start -> Run -> cmd IPCONFIG The "gateway" address is the IP address of your router.
Some routers are slow at starting the web configuration and need a "/" at the end of the URL. It sometimes helps to ping the router first.