I had a similar issue with linksys. My wireless usb adapter although showing a connection to my wireless network, would not get me online. Now I'm no genius and I'm not saying THIS is the answer, BUT I did manage to get it working after a few minutes.
First be absolutely sure your wireless router is working. Make sure whatever pc is connected to it (if any) is able to get online. If you just have it connected to your cable line and have your only pc in another area with your wireless usb connector...try connecting your pc directly to the router just to make sure your router is working properly.
If you're already 100% sure your router itself works then just unplug the power from your router and power down your pc. Get the router back on and power your pc back on. Wait for the indicator lights on your usb adapter to stay solid.
The mistake I made was... once you enter the wireless network key, you don't have to enter it again each time you boot up and start your machine. You will just stay connected and don't have to bother doing it again as entering it again while already connected will DISconnect you. At least for linksys that's what happens.
So everything works fine now for me. Hopefully I mentioned something that may help you. If not, don't worry...lol someone here will have an answer for you. Good luck.