Had the same problem. Turned out the shutter button was stuck in half-way down mode. Pressing the shutter button took a picture, but then the button only released half-way, preventing the rest of the buttons to work.
I pressed hard and slightly sideways on the button a few times, changing sideways direction for each press. That unstuck the button.
If you have similar problems, it could be a different button. Try the same procedure on all the buttons, preferably with the camera turned off.