You will need direct access to the back end database to correct this issue.
Once you have admin level access to the dabase you can run the following queries
To check for the deactivated site run
select * from group_ where active_ = '0';
The default site should be named Guest by default. You can get the <groupid> for .this row
Then run the following query to reactivate group
update group_ set active_ ='1' where groupid=<groupid>;
NOTE: replace <groupid> with the actual value.
Then you will need to restart wasp and I believe this should correct your issue.
Release: CNMSPP99000-7.6-Unified Infrastructure Mgmt-Server Pack-- On Prem