Hmm, couldn't say why it happened. Probably was better that you had it off while you were away- imagine if it did that when you were away... could have set your house on fire.
As far as replacement motherboard... just make sure it can accept your current CPU; or get both a new CPU and a new motherboard... heck use this for an upgrade oppurtunity (if you can afford it).
Hard drives, optical drives, and expansion cards would likely work in any motherboard.