Have you tried inserting it into another USB port?
To get mine working, I had to download the drivers from this link;
http://www.ralinktech.com/support.php
The chipset included in the DWA-140 is the Ralink RT2870 drivers, so click the first link on that page and try giving them a download. I found the D-Link drivers were worthless, but thankfully installing those Ralink ones seemed to fix my recognition issues.
