Or if you leave it unattended for too long...
I didn't think that mattered... how long unattended? I assumed it would just sleep until the battery dies. I've accidentally left mine powered on on my desktop for days, and when I went back and noticed, I touched the shutter and the screen came back on.
That's true !!!
After I read replies about "...leaving it for too long" I told myself "that might be it" so I tested it again pressing the shutter button halfway right when the screen turned off but again it didn't turn back on
It's not a big deal but so annoying to me. It's not a cheap camera and you expect something as simple as this works flawlessly :p