Can't set autopower on

I have managed all the other functions on my Sansa m250 and love it. However, NOTHING I do, including following instructions, turns my autopower function ON. I would like to have the player turn off automatically after 30-60 mins every time I turn it on. (It seems you have to set the sleep timer each time, but the autopower function ought to work without resetting each time, no?) I can get to the auto timer, I can set the minutes, I just can’t get it to register “ON”. Thanks to anyone who can decipher my problem and help.