We have single use licenses on win7.
When we have power outage many times the license become un trusted and cannot be repaired.
It never happens when we shutdown the power only when their is power outage.
Some cases the license is not affected, some other time it can be repaired but many other times it just lost and need to be released by esri.
If you know the Authorization code used in each machine, you could clear the trusted storage, and reauthorize the SU license.
But an important thing to do is to connect all the machines to UPS.
Thanks but as far as I understand if you registered the license once it is written as used in MyEsri and can not be registered again even from the same machine.