Open "services.msc" and check which services the vCenter Server Service depends on and whether these services are started. If not, check the Windows Event logs to see if there are service start errors.
Please look at the following vmware article and see if this helps.
first you check vCenter Server database size exceeds the maximum limit or not.if yes then reduce the database size if not then take a database backup and go through srijits link step.
As Subhasis2009 said generally we get this error due to VCenter Database running out of allocated Transaction log space, And this can be fixed shrinking the Trans logs or freeing up the space (Make sure we take the backup of the database/Trans logs before shrinking the Trans logs)