Why won't my car start

What is your question?

My 2000 Buick lesabre had a clicking sound and then all lights on dash and interior and headlights began blinking on and off killing the battery in the process. The clicking was coming from fuse box under the Backseat had someone who know about cars tell me it's a relay fuse and to go buy a new one but he said it might fix the problem need more than a might any suggestions