[Christ]

replace the main relay.. end of story.

If it only does this sometimes, or most of the time, start watching when you turn the key on where the check engine light is.. if it comes on, and doesn't go out after a sec or two, or it doesn't come on at all, or you don't hear a click when you turn the key after a second or two (turn to "on", but don't try to start") then replace the main relay, and you'll be good to go.