Why wont my ls400 start after putting a new battery in? on 1992 Lexus LS400

I had a 5 year old battery in my lexus and accidently left the head lights on with car off for about a hour and completley killed my battery went and bought a new one and it still wont turn over. I've noticed that my spark plugs have been misfiring but have failed to replace them. Could it be spark plugs or ignition?

I would have the battery cables cleaned and tightened first, Who installed the battery?