What type of database do you use? The embedded one, or the PostgreSQL coming with the vRO appliance, or some external DB? If I recall correctly, there were a few reports in the past that embedded DB sometimes got corrupted, or that after a restart a different database got selected. Please verify in vRO configurator that your DB configuration hasn't changed after the reboot.
Also, could you check if the configuration resource is completely missing or its content is corrupter? Open vRO Java client, switch to 'Design' perspective, click on 'Resources' tab in the left pane, navigate to Library->REST->Configuration. Is there some child node labelled with a guid string? If yes, then the configuration is still there, but its content is corrupted. In this case, click on the node and then on 'Viewer' tab. It should open a XML document with configuration data; could you send it to us to take a look?