If you cannot find the power button, just simply remove the battery wait for few seconds and put the battery back. What I assume of this behavior is 'If the coming out lens is obstructed by anything' the camera will show such error. If it does again, I would suggest calling Sony and getting their advice. Regards
Common error, can be caused by altering images or editing in the computer, then saving the images back to the memory stick, the camera cannot read the edited images or sort out changes that may have been made to the file allocation table on the stick. Download all the images to the computer, back the images up to a disc, flash drive or another hard drive. Then re-format the memory stick in the camera before using it again. The image "workflow" fr digital photography intends for the camera to PC path to be a one way street.