It can be due to these reasons,
Either your wireless adapter is disabled physically or under Network Connection. Solution: Check for any physical switch or button on your laptop that has a Wireless symbol on it and turn is ON. Also type ncpa.cpl in the RUN window right click on the Wirless Network Connection and Enable.
Wireless adapter drivers are missing. Solution: Go to your laptop support site and download the latest wireless adapter drivers and install them.
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WiFi Speed Test