iMac won't go to sleep?

jammadave wrote on :

hey guys - i have the Mac set to go to "screen effects" after a half hour and sleep after 3 hours.

now, sometimes, lately (not all the time, just sometimes), i walk into the room and it's either just on screen effects, or worse, hasn't strayed off the actual app i left it on. Now, this may not be as bad for flat-panel displays as it is for CRTs, but still...

what could that be?

i've only had the iMac for a couple weeks and have installed only a couple apps...

thx dave