Hi stanclayton,
Did you ever turn your keyboard topsy turvy and tap it, what did you find? A lot of dust. Did you ever open the housing of your computer and what did you see? Again a lot of dust. What do you think that ruins computers if there is too much of it. Exactly dust.
Together with the things Igor mentions here, and the fluctiutions in the mains. These are the main causes of burnt down hardware.
A virus can eat your data or corrupt your data so as to the effect your computer do not function anymore, but viruses as far as I am aware do not eat hardware.
polonus