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