1. Did you add your vCenter VM in domain and then you installed vCenter on it ? if Not, you will have to first add your domain as identity source into SSO(This can be done only through web client : use default user: administrator@vsphere.local, if its vCSA default would be "user: root/pass: vmware") & then you will have to give vCnter admin privileges to domain administrator user .
2. If Yes, please try login using webclient instead of VI client. (https://<web client IP>:9443) (If you installed all vCnter component on the same VM, then VC IP itself is web client IP, same for VCSA). Also try giving complete domain name like "VC01.com\administrator etc. (whatever is your domain).
3. If you just try "administrator", it would be local OS(The VM on which you installed VC) admin user not the domain admin user . At-least you should be able to login with this user: administrator@vsphere.local (its default SSO domain)...if its vCSA default would be "user: root/pass: vmware"
Let me know if you still face the issue.