My mac book air wont connect to internet and the wifi button wont turn on

Try rebooting the laptop. Sometimes a simple reboot is all that is needed.

Try booting into Safe Mode which will prevent third party software from automatically launching during boot & login. Usual culprits are anti-virus software, cleaning apps, and third party security software, none of which are needed on a Mac. However, if you have any of this software installed, there is a possibility that some preferences may configured such that even if this software is not launching in Safe Mode, it may still be blocking macOS from connecting properly.

Also try creating a new user account, log out of your main user account, then log into the new user account. See if that makes any difference.

Make sure the WiFi hardware is seen by macOS by checking the System Profiler which can be accessed by Option-clicking on the Apple menu and selecting the first item.

Here is an Apple article for troubleshooting WiFi issues:

If your Mac isn't connecting to the internet over Wi-Fi - Apple Support

Until you resolve this WiFi issue, you may want to try connecting the Mac directly to the router using an Ethernet cable and any necessary adapter. This will bypass any hard to troubleshoot WiFi issues until you can figure out the problem.

Also, please don't create multiple threads for the same issue as that can get very confusing to the people trying to assist you and wastes our time when people will see just one thread and provide the same information as someone else has done with the second thread.