This article is explaining what you would need to verify in the instance of your EPOS not opening and what you could action on.
What to verify
Check the network
Verify the network as the modules have to be able to reach the server via the network.
Check with IT
Contact in house IT as this may be related to a global network failure.
Run Standalone mode
If you have excluded the above, in the EPOS module:
Click on Network offline.
This will run the EPOS in the standalone mode.