1999 Volvo S70 cranking

Car wont crank (turn over), clicking noise coming from starter; tried jump starting, still clicking; wrecker tried jump starting car, engine turned over a little then the clicking resumed with burning odor coming from engine compartment; after removing starter the smell was coming from the starter. The car had only been sitting for 30-40 minutes, not starting problems before then. I replaced it with a used starter, still clicking. Just ordered a new starter. Where do I go from here, anything else to check before installing the new starter (to be delivered Friday, 1 Aug 2014).

Thanks in advance