Power Up Problem
I almost thought I wrote that myself, except that it's signed Darren (UK). John (US)--that's me--had the exact same problem.
I bought my z120 as a factory refurbished, didn't hesitate to send it into Casio Repair, and it came back twice, not fixed though they tried repairing the circuit board on the first try, and replacing the circuit board and firmware on the second try.
I hear the standard policy is for them to replace the camera on the third try, which I just sent it back in for (and the person on the phone said the third round replacement is the standard).
Note that even though my camera was factory refurbished, and bought on Amazon from someplace in California, Casio did not hesitate to honor the warranty and I did not have to go through the seller to get this done. I've been sending it to Casio Repair directly.
Anyway, glad to know I'm not completely bonkers--even though I'm a Yank.