"the manpage can tell you everything you need to know........."
That was well worth a wasted ignorant post, I'll help, Ice: (Maybe that's why this board is here?
You're probably trying to setterm within an X session, this command only works on the linux console. Bet if you try it on the linux console, you won't get an error.
If you want to change DPMS sets in X, the command is xset. In the startup config of your X window manager of choice, you probably want xset -dpms
That should do the trick!