A guaranteed way to make a receiver or amplifier fail is to create a short circuit by improperly connecting speaker wire to your speakers or receiver. It could be as simple as a stray strand of wire which has come loose from the binding post (on either receiver/amp or speaker) and touched the other terminal. It is critical to make sure that the bare wire of the positive speaker cable does not touch the bare wire of the negative speaker cable.
Discuss "Tip of the Day: Short Circuits" here. Read the article.