If one-button mode is enabled on your camera, it will begin recording automatically once it's powered on.  This will be indicated by your camera's LCD screen blinking and the red LED blinking on the front of the camera if you do not have BLF enabled in the settings menu.  A good test to see whether or not you're in one button mode is to hold down the shutter button for 2 seconds and let go.  If "SEt" appears on the camera's LCD screen, you're in one-button mode.

To exit one button mode, please turn on the camera so it starts either recording or taking the photos.  While it is doing so, press and hold the shutter button for 3-4 seconds, then release.  The camera should stop recording, then display "SEt".  Press the shutter button once to enter the set menu, then "onO" will be displayed.  Press the shutter button again to switch it to "onF" and the one button mode on your camera will be disabled, and you should be able to turn it on as normal.