Picture is Sideways (by 2 users)

The picture on my monitor suddenly went sideways and I cannot get it to go back to the regular orientation. I tried to shut off the computer and turn it back on and also shut off the monitor and turn it back on and turn both off together but this did not work. I went into display in the control panel but there is nothing there to reverse the orientation. How do I fix this. My neck is getting sore!