Thanks everyone, I'll try your suggestions.

Just one question: can iMacs turn themselves on? I distinctly remember shutting it off before I went to bed. When my alarm rang, I noticed that my whole room was bathed in blue light. Yup...the iMac was on. Not even sleep mode, it was on. It's possible that someone did it manually, but are iMacs on timers or something? Is there anything that can explain this?

-Apostrophe