Have spent countless hours trying to resolve this problem --- my Sony Vaio simply would NOT pick up a wifi signal right beside the router.
Changed Drivers up an down --- removed the adapter and reinstalled it ---- NO change
Read every bit on the web about the issue --- netsh.exe resets etc ---- NO change
Finally found a glimmer of hope --- apparently 2013 version of ZoneAlarm could be the culprit (not compatable with Win 8.1)
Updated Zone Alarm to 2014 edition and miraglo wifi recognised again --- Hope this helps somebody