We had a pretty severe thunderstorm coming through last night and this morning, the P12 is completely unresponsive. I checked all the outlets in the room and they are all working fine. I reset the breaker at the box just in case.
Turning the master switch off and on on the P12 doesn’t do anything. Same goes for hitting the white reset on the back next to the master switch.
Any idea of what to do next?
Fyooz?
Sorry @RonP, I speaker a few different languages, but that’s a new one to me. 
Check the fuse in the back panel of the P12.
For clarity, see @Clarity’s suggestion…
Look at it this way, the P12 saved you grief by protecting your gear. Which likely would have been torched. I don’t use a P12 myself, but I thank those who designed and built my Furman SPR-20i every time a super cell passes over my domicle in Chicago. Betting it’s the fuse as RonP and kclarity suggest. 
If it wasn’t the white breaker in the back, it’ll almost 100% be the fuse. It’s definitely the first thing to try.
Fyooz
Hope it wasn’t an M1.
Or a Purple.
I think it’s indeed the fuse… no reading on the multimeter.
Luckily, this was the stock fuse, so a perfect opportunity to change it out to a Synergistic Orange (was planning to order one eventually… this just pushed that time table up a bit)
Update: Replaced the fuse (got a SR Orange) and magic, the P12 is back!
This is exactly why it is important to have the correct value fuse installed. If you had substituted a fuse of a higher rating there is a good chance the transformer on the power plant and possible circuitry past it. I see people running 2 amp fuses when the device calls for 1.6 amp. I guess they are willing to gamble.
Actually, you can run a slightly larger audiophile fuse, but check with Paul in advance. Stock fuses are cheap, stock sizing makes sense in those cases.
You can do that if you are willing to gamble. If it fails to protect the transformer a manufacturer could choose to void the warranty. Any fuse that sells for big bucks most certainly be accurate in value. If they don’t offer the correct value choose to be on the safe side and avoid the fuse.
Paul McGowan approved my use of a one size higher slow blow fuse in my P12 and P5. I asked him upfront before installing. I’ve obtained similar approvals from other manufacturers.
Other manufacturers have declined, requiring the exact spec fuse.
And when I had one, he also approved a DS Jr. upsized fuse (he approved 1.25a, versus 1a).