Install the motherboard driver package and then reboot, try that driver and device again. Also, use the rear USB ports.
Hi I have a Desktop XP Machine which I am trying to install a Ralink USB RT73 too.
I installed the drivers that came with the device and inserted it when prompted, then up pops the device hardware wizard saying that :
802.11 n wlan is not found.
I have Service Pack 3 in the PC and everything else is ok.
Tried the device in a friends house and it works, so no malfunction there.