when I scan for my airport express wirelessly it can not be found and blinks amber, but when connected by ethernet all is fine.

When I scan from my pc for the airport express wirelessly it can not be picked up. When I connect it via the ethernet the scan still cannot find the device. Although when it is connected by ethernet it is picked up and a wireless nextwork can be set up through my iphone, ipad etc. I want to use this as a range extender, any ideas why my pc isn't picking it up? I've double checked for updates/latest software/etc. Help is appreciated!!