Hawking HWUG1 adapter and Compaq Deskpro EN p800

After trying different PCI Wifi adapter cards that wouldn't work with this computer, I went and tried the Hawking HWUG1 USB wireless adapter. I installed the software as recommended by Hawking. I am using an external roof mounted 2.4Ghz Yagi and still cannot find networks. My daughter can sit in her room with her Toshiba laptop and pop off 4-5 local networks. I can do the same on my Presario notebook. I know the adapter is Txing by using a Wifi detector device, but not Rxing, or at least it's not being processed. Nothing comes up. Any ideas? Is COMPAQ DeskPro EN motherboard too old? What would I need to do to correct it. I love this dinosaur and don't want to give it up! What motherboard & processor would I have to upgrade to? Am I missing something? Please, I really need some help with this one. I've tried everything under the sun. Thanks!