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?

Asked by for the 1992 Lexus LS400
I would have the battery cables cleaned and tightened first, Who installed the battery?