Defender Service will not start (4303266)

Some possible options to assist in reviewing an issue with the Defender Security Service failing to start:

-Review for any relevant events in the Windows Event logs when the service is started.

-Review the Defender logs for any errors; if the service is not starting it is possible that no current Defender Logs are created.

-Running "sc query dsservade" after a failed attempt to start the service should return the Windows Exit Code; more detail regarding the exit code can be reviewed via "net helpmsg {exit code}" or via further research online.

-Attempt to start the service manually from the command line.  This may reveal further detail.  For example, open a CMD.exe console on the server, navigate to the folder where Defender is installed and attempt to start the service from the command line by entering "DSServADE.exe" This may reveal further detail regarding the issue.  If this indicates missing dll files (such as dssnet64.dll which would typically be located within "Program Files\Common Files\One Identity\Defender"); then it may be required to re-run the Defender installation also ensuring the "Administration Console" is also installed.

-Failing the above, ensure that the server where Defender is installed does not have any outstanding updates and reboot.

-Antivirus or similar software may be blocking the service; review any relevant antivirus software logs for evidence of this and exclude Defender if possible.

-Testing the installation on another server, or removing and reinstalling Defender may also be further options.