System won't auto-sleep

For some reason, my Mac won't sleep automatically. I have the Energy prefs set to sleep after 1 hr of inactivity. I go to work, come back hours later, and the machine is not in sleep mode. Any idea why? I had to deal with that crap with Windows.. now my Mac is doing it too? Hmm..

Anyone? (PS, it's a Mac Pro)

Also, even though I do NOT have the option "put hard drives to sleep," I still hear them wake up once in a while even if I was not in sleep mode.

I might have to call up Apple support.

Only issue like yours I have ran into was some external USB device not letting it sleep. Do you have any external USB stuff plugged in besides normal Keyboard/Mouse?

Anything interesting in your Console? It's in your Utilities folder.

I've seen this happen when you leave certain USB optical mice plugged in; it'll sleep but half a second later the mouse wakes it up again. I'm sure other devices might do the same.

Hmm.. no, nothing plugged in that wasn't plugged in before. This started happening randomly.