Hi Alaa,
Dave has described your current configuration exactly.
As it currently exists, only Norton is supplying your "real-time" protection, for the reason
that Dave has explained. And Windows Defender is deactivated.
However, you can configure Windows Defender into "passive" mode, which will allow it
to perform scans. On the Windows Defender "Virus and Threat Protection" screen", you should
find a "periodic scanning" button. (scroll down to see it.) If you turn this switch "on", Windows
Defender scans are available, but not "real-time" protection. Windows Defender "Offline" scan,
can be a very useful tool in certain situations.
Regards, Glen