The power failure probably caught it in the middle of a write process to the uSD card. You can try to reload the OS on it...using Etcher which does it all in one step...but the uSD card may be borked in which case, you will need a new one. A top brand, 8G or larger and Class 10 or better, as in SanDisk or Samsung or...from a reputable vendor.
I guess you're right. It's the third or fourth time I have to do this (reinstall the OS) due to a power outage... Is it something I can avoid using a different uSD brand? Currently I'm using SanDisk Ultra Class 10.