This is a tricky problem. There are various reasons for this, please follow the below wordkarounds in order to resolve the problem.
1. Make sure your Wi-Fi is turned on (Some laptops have hardware switch as well).
2. Restart the laptop and try to start the hotspot again.
3. In Windows 8 and above, turn on the flight mode and then turn it off.
4. Open Network and Sharing Center -> change Adapter Setting -> right click on your Wifi Adapter -> Properties -> Advanced tab – > Click on Adhoc support… -> set value – Enable.
5. Finally, if the problem still exists, disable power saving mode for WiFi adapter.