Which password was changed? Was it the passsword for the account that ePO uses to access SQL? If so, you may need to manually edit the db.properties file to set the new password. Try this:
1) Stop the three ePO services on the ePO server.
2) Make a backup copy of db.properties, located under the ePO install folder at ..\server\conf\orion\db.properties
3) Open db.properties in notepad
4) Locate the line that starts db.user.passwd.encrypted=
5) Remove the .encrypted from this line, and replace the hash value with the plaintext password for the account. So if the password for your account is "epopassword", you would change (for example)
6) Save the changes to db.properties
7) Start the ePO services again.
If all goes well ePO will be able to connect to the database again and you should be able to log in. If you check db.properties, the plaintext password should have been replaced by the new hash value.