There are many reasons for this problem; one of the reasons is that Windows Update failed to install or update the Network drivers, in that case, you have to update the required driver manually.

I figured out how to automatically connect my Macs to my NAS on login, easy peasy. However, after rebooting my NAS, I always have to manually reconnect my Macs to it. Conversely, I have this NAS ...

Resetting my phone's network settings has saved me many times when I thought something was seriously broken with my Galaxy ...