Problem connecting to wireless network

I have linksys wireless router upstairs connected to desktop, laptop w/internal wireless card, linksys range expander, linksys usb wireless adapter connected a desktop downstairs (one level)I updated latest drivers and firmware from linksys for everything. Took the laptop downstairs next to desktop w/usb adapter and get excellent sig strength from router via expander, but the desktop gets no signal at all and can't connect to access point. Please help