If you go to Control Panel, then Device Manager, is the wireless adaptor been detected properly? If yes then, try to update the drivers; run Windows update from StartMenu>All Programs
Click on Check for updates on the top left. Once the checking is finished, click on Optional updates are available. Can you see the wireless adaptor on the list? If yes, tick it and Click Ok. Once installed, restart your system.
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Is wireless isolation enabled in your router? If it’s then you need to add your new system’s MAC address to the list else you cannot connect.
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Double check that you entering the correct web security key (this case sensitive).
You can check your web key, by entering routerlogin.com into the bowser from your XP system or 192.168.0.1 , the default account login settings are as follows, (lower case)
User name: admin
Password: password
Now select Wireless setting on the left landside. More information in the manual
http://kbserver.netgear.com/pdf/dg834gt_manual.pdf
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If problem persists try to use different security option, you can choose from WEB, WPA-PSK etc. if you do this remember you need to re-enter the web key into your other systems.
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Updating the firm is a good thing too
http://kb.netgear.com/app/products/model/a_id/2328
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Do change your router default login password .