Changed batteries and it doesn't power up after that.

"I found the solution on the apple forum:

Take all Batteries Out.

Roll up a small piece of Tin Foil about the size of a Pea.

Drop the Tin Foil Ball down the Battery Compartment.

Put your Batteries Back In.

You should have a Working Keyboard.

This worked for several people on here including me.

I'm still running 2 months later with my rolled up piece of Tin Foil in my Battery Compartment.

I know it sounds Crazy. That's what I first thought.

Apparently Apple did not make the + Terminal Inside the Keyboard correctly.

Try it. What have you got to lose?"

I encountered the same problem. I was mislead by the "dummy battery" inside the battery compartment, think that it was positive terminal facing upwards. So naturally when inserted battery with positive terminal facing the lid, it will have wrong polarity. After I reverse the battery terminal, with positive terminal inserted facing down, keyboard works like a charm. Really a silly and misleading design. First it misled me into thinking that there is a third battery stuck inside, second it misled me into aligning the wrong polarity of the battery as I did not notice the polarity when I remove the old batteries. Hope this sharing helps!

I tried the pea-sized foil, several different "pea" sizes... Each time, the green light came on for a second or 2 then started blinking--33 times blink-blink, then finally the green light went off altogether.

"I tried everything. Almost went to buy a new keyboard. ( mine is probably 5 years old )Luckily I read about the tin foil , tried it and IT WORKED!!

had to put in a code but it’s working !!"

Bad replacement batteries?

"I had this issue after spending the better part of a day removing severely corroded batteries. I was devastated to find it didn't turn on after all the work I put in.

I looked at everything more closely and noticed a key thing. The screw holding the logic board into place is the negative terminal for the batteries! When I put everything back together I didn't tighten that enough *and* I had a bunch of dust and crud in the screw threads on the end cap as a result of the cleaning. I gave it a good rub with a paper towel and Q-Tip and voila! Back in business!"