I had also a big surprise with my old Optio-S (series of 2003 or 2004?:
without any warning or any sound the lcd went black, camera went dead with the lens stuck out.
Only sign of life was the green led around the on-off button, this led was lit on.

Tried fresh battery, nothing.
tried pushing all the buttons, nothing.
tried leaving overnight without battery (to empty condensators ??) , nothing

Then read all forum messages on this website, bingo!
I noted all the possible solutions and had good luck on the first try: try another SD card. BINGO !!!!!!!!!!!

When i read the old SD that was on the camera when it crashed then i see in windows all the pictures but also a lot of garbage files with funny filenames like russian signs. Clearly currupted files garbage!
That must have been the cause because now the camera works fine.
I think the camera made these funny files and then it crashed.

I will try to clean or format the old SD but i dont really care about that now, it costs only 15 euro.

I hope this helps you out there!

Bob

ps: just to be complete i list the other options i was going to try:
-try fresh SD card
-format camera (it needs to work first!?)
-format old SD and try it again
-update firmware in camere (it needs to work first??)
-press all the buttons a lot more.
-soft blows agains camera
-finally: let the dog try it