Heres' anothe item to check for in BIOS Setup, probably in the power control configuration settings. On most mobos there are several options for automatically re-starting a macine that is "shut down". These watch for incoming signals on particluar devices and initiate a start up when there is new acivity. Often these are labelled by phrases like "Wake on ....". They may include Keyboard, Mouse, FAX, Modem, LAN. That last one will respond to any activity on the LAN port (or maybe a WiFi system?), and you probably do have a network connection somewhere. For any that you do NOT want to cause a start-up, disable those, then remember to Save and Exit.