Make sure there isn’t a key combination to disable WiFi like Fn+x
If all else fails you will need to get that machine online somehow. So either use a hardline to the router or use your cell phone as a tether. Then you can try another kernel. If that is an intel wifi adapter they are having issues on the newer kernels. Once online you can try:
sudo pacman -S linux-lts linux-lts-headers
sudo grub-mkconfig -o /boot/grub/grub.cfg
After reboot you should see 4 entries in grub. linux linux and it’s fallback image and linux lts and it’s fallback image. Select linux lts and boot into the system and see if you have wifi.