Hi,
You can follow the official documentation on how to restore the SCOM databases over here:
How to Restore Operations Manager Databases
Here are also the official documentation for disaster recovery which should cover everything you need to know:
Disaster Recovery in System Center 2012 - Operations Manager
Disaster Recovery Command-line Parameters
If you've followed the above documentations precisely, then I would start by investigating the Operations Manager event log for more clues.
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Best regards,
Leon