Are you sure your device got wifi swtich ON (it could be a physical button or a fn+fkey combo)?
Are you sure you aren't in plane mode? Tap on Notifies icon near the clock, and check Icons : disable Airplane and turn on WIfi
go to settings > networks > wifi. If under networks no wifi option is shown, then there's an issue with your wifi adaptor
Check under device manager to see if there are any issues with the wifi adaptor
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