my computer self powers up in standby mode

I have an inspiron 600m laptop.  I left my computer sitting at my desk in standby mode (I am sure it went into standby mode) and no one was home.   When I came back, I noticed that my laptop was on with the fans in full blast.   The screen was on but nothing appeared and my laptop was extremely hot.    I am wondering what is causing my laptop to randomly wake itself up from standby mode.  I checked the bios, all the auto turn on stuff were disabled.  This wasn't the first time it has happened to me either.  Can someone shed some lights on why this is happening?