Started stays engaged on 2001 GMC Savana 2500

Went to start my van and battery was dead. Got a jump and van started, drove for approximately 30 minutes. When I shut it off I restarted it a couple of times, worked fine. A couple hours later I went to start it and the battery was dead again. Tried jumping it again, but as soon as the jumper cables were put on the started engaged and began cranking the engine without the key. Was told it was my starter so I changed it, same thing, new battery, same thing starter stays engaged.

Asked by for the 2001 GMC Savana 2500
I think that damage may have occurred to the electrical system when the jumpers were put on the second time. I recommend towing the car to an auto electric specialist or a GM specialist.
If you want to find a specialist, here's a directory link for you:
I found the problem, after i also changed the inigition switch. Wasn't the switch however, the problem was that at the point that the wiring harness crosses over the engine right to left it had rubbed through the harness coverning and into two wires, thus supplying constant power to the starter. I seperated the harness repaired the wires rewrapped the harness and all iis good in my world, thank you.