What is the error message you get when try to start?
It normally fails to start if it fails to connectivity to database server. You may get some clue in server log.
When did the issue start and what changed? If only after a reboot, is sql on the same server? Sometimes it is a timing issue where the eventparser starts up before the sql server does. If reboot was due to any windows updates, what version of epo? Some security updates have been affecting tls and cipher suites, which can affect logins. Can you get into the console and is it functional? If event parser won't start, then I would venture to say the answer to that is no. If any password has changed, go to https://servername:8443/core/config (substitute your servername and port) and reset/test connection there. If it was due to windows updates, was the sql server also updated and rebooted, if separate server? If so, did you restart epo services after sql came back up?
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