@phuchhepepsi: I have the same problem with my L4.
It fails to start up sometimes.
Replacing the batteries did not work.
Taking the batteries out of the camera for a few minutes and the "on" button works again.
I think the problem occurs more often when I used the flashlight.
I cannot check it anymore because I brought it back to the shop last week for repair/SW upgrade or whatever. (1 month they need for this and they said this "once in a while problem" might not be found by the service centre)
Let's hope it is repaired because it is a good camera.