Quote - "Please explain how running a computer harms the environment.

Well there are a lot of nasty materials that are used in the manufacture of computers, and if you throw an old computer into a landfill thats technically a contamination of the landfill. ok i suppose its just a trace contamination, but its still a contamination...

Also your power supply can play a large part in how environmentally friendly your computer can be, cheap power supplys have poor efficiency, in short they need more mains electricity to convert into the power that your computer needs which is very wastefull. these days its best to pay that little bit more for a high efficiency power supply... the power supply in my computer has roughly a 80 - 90% efficiency which means its drawing less power from the mains which saves me money in electricity bills, also it helps the environment :D