A leak in the 2nd floor bathroom made its way down the inside of a wall to the GFCI of the 1/2 bath downstairs.

I have since replaced the GFCI and wired it according to the package provided diagram.

An electrician replaced the GFCI in the 2nd floor bathroom and it worked for a while. He examined the GFCI in the 1/2 bath and said that it was wired correctly but I should have placed the receptacle upside down (Don't know what that's about).

Neither of those GFCI's work now.

My guess is that something on the circuit has an electrical issue. I am having a hard time figuring out which item it is. Obviously some outlets stopped working but other than that, everything else seems ok.

Can anyone suggest a good troubleshooting method that can help me discover the culprit?