Hello!
Did You try to create a Storage Domain and it didn't work? Because the docs say:
"The data center requires a functioning cluster, host, and storage domain to operate."
(from https://www.ovirt.org/documentation/administration_guide/#Data_Centers)
That means You have to have at least one Storage Domain configured in order for the Data Center to be usable.
So I would start with that. 
HTH,
rob