Hi,
Customer should always back their policy store on regular basis.
I generally recommend multiple method to back up a store, XPSExport, dxdumpdb, as well as physical installation directory.
Customer's business is at high risk, when there is no store backup, because you will never know if you are able to recover during this time round of data corruption. We have seen customer's SQL store is corrupted to such state only rolling back store image is able to recover.
So, before you try to figure out if and why admin ui can not login, could you verify now is it even possible to run either XPSExport, dxdumpdb command successfully?
Fixing admin ui login is different topic, even if can not login admin ui, you may still be able to change the realm value simply by using XPSExplorer tool and alter the value there, but you need to know what you are doing at the command line.
Thank You,
Hongxu Liu
CA Single Sign-On Support