When I tried connecting or logging into Symantec Endpoint Manager, I found out that I weren't able to login. A message kept popping up displaying " Unable to connect to the database." and when I click "OK". The dialog box will close and I would not be able to login. There is an attachment that shows the issue I am encountering.

I tried the following steps

Verify if there is any running instance of dbsrv9 in the Task Manager > Processes tab. If yes, then end that process

Start the Embedded database service. ( If this does not resolve the issue, then follow the steps listed below )

Go to "C:\Program Files\Symantec\Symantec Endpoint Protection Manager\db\" and rename sem5.log to sem5.log.old

Click Start, click on Run and Type "CMD" then click OK

In the Command Prompt type: "CD C:\Program Files\Symantec\Symantec Endpoint Protection Manager\ASA\win32\" and press Enter this will change directories to the folder containing dbsrv11.exe.

To force the recreation of sem5.log. Type: "dbsrv11 -f "C:\Program Files\Symantec\Symantec Endpoint Protection Manager\db\sem5.db" and when I press Enter the following message has shown

Must specify one database with -a or -f options.

what should i do next?

first try a repair from add/remove programs.

Have you try repair in add/remove program ?

You can try it for 12.1

Error when logging to Symantec Endpoint Protection Manager: "Failed to connect to server". Unable to start the embedded database service.

Version 12.1.2xxx:

1. Stop Symantec Embedded Database and Symantec Endpoint Protection Manager services in theServices.MSC.
2. Rename sem5.log to sem5.log.old
   Path, for 32 Bit: "C:\Program Files\Symantec\Symantec Endpoint Protection Manager\db\"
   Path, for 64 Bit: "C:\Program Files (x86)\Symantec\Symantec Endpoint Protection Manager\db\"
3. Click Start, click on Run and Type “CMD” then click OK
4. In the Command prompt (as Administrator if applicable): 
   For 32 Bit, type: "CD C:\Program Files\Symantec\Symantec Endpoint Protection Manager\ASA\win32\"
   For 64 Bit, type: "CD C:\Program Files (x86)\Symantec\Symantec Endpoint Protection Manager\ASA\win32\"
   and press Enter. This will change directories to the folder containing dbsrv12.exe.
5. Force the recreation of sem5.log. 
   For 32 Bit, type: dbsrv12 -f "C:\Program Files\Symantec\Symantec Endpoint Protection Manager\db\sem5.db"
   For 64 Bit, type: dbsrv12 -f "C:\Program Files (x86)\Symantec\Symantec Endpoint Protection Manager\db\sem5.db"
   and press Enter.
6. Click Start, click on Run and Type “Services.MSC” then click OK and start the Symantec Embedded Database Service
7. Start the Symantec Endpoint Protection Manager Service.
8. If it stays started then go ahead and log into the Symantec Endpoint Protection Manager and everything should now be working properly.
   OR
   If the Symantec Endpoint Protection Manager service fails to start then run Management Server Configuration Wizard in order to log in to the Symantec Endpoint Protection Manager.

No I didn't try repair, I will try and revert back u Mr.James007 & AJ_01.

Please post catalina.out and scm-server-0.log files

Available here : C:\Program Files\Symantec\Symantec Endpoint Protection Manager\tomcat\logs\

I did mention that at the very beginning , please try repair first, if it does not work will try other steps

Follow the article for the disk space

Disk Space Management procedures for the Symantec Endpoint Protection Manager

https://www-secure.symantec.com/connect/articles/issue-related-low-disk-space

https://www-secure.symantec.com/connect/articles/symantec-endpoint-protection-manager-121-database-using-high-amount-hard-drive-space

http://www.symantec.com/docs/TECH166923