please describe exactly how do you install the dbconnect app and what you see in the Splunk interface after you first logon.
Where the problem laid exactly? Is it dbconnect is not properly starting or a whole splunk instance?
Did you check Splunk user permissions of the DB connect folder?
What OS are you using? Is any antiviruses or selinux is switched off for the Splunk folder?
Did you try to switch on debug logging for the dbconnect app?
Did you try to restart splunk instance after rebooting the OS (ensuring no one processes are blocking network ports)?
What in dbx.log and splunkd.log around of startup process?