So, it sounds like you need to reset the account ePO user to access the database, but can't get into the GUI to do so, right? I'd suggest setting up a separate service account that connects from the ePO application to the database.
First, go to this directory:
[ePO install directory]\Server\conf\orion
Open db.properties. This file includes database configuration information.
Replace db.user.domain and db.user.name with the account you want to use to connect to SQL server. Change the "db.user.passwd.encrypted.ex2" filed to "db.user.passwd" and replace the password with the cleartext password of the account you're going to use to connect to the DB. Save the file and restart the ePO services.
Now, reconnect to ePO on the <servername>:8443/core/config URL. Configure the same account again through the GUI, and save the changes. This is an important step, because it will update the db.properties file and replace the cleartext password with the encrypted password.
That should cover it.
I change db.properties accordingly on my domain account but it didn't work...but i try to reset password of my co-worker that already resigned and edit password on epo db.properties, now i can open the page/console...i think i must create epo domain user separately to link db.account so that this problem wont happen again for future system admin on this company
I would strongly recommend you edit your posts to remove all sensitive information; it's extremely common for attackers (or even malicious co-workers) to read forums like this looking for sensitive information, like your password.
In any case, sounds like you figured it out, glad I could help.