Hi,
The only thing that i am thing that the database came up and is running as sap system can connect it.
Can you see any alert in the alert log of the database. If yes please post it.
If not issues in the db alert log So database is not an issues
Can you please check this note . I know that the version of the note is quite old. Can you try to set the below parameter.
for the below code returned
Note 81499 - No reconnect after offline backup
Just some suggestions... 
Thanks
Rishi Abrol