The key in its first position makes the electrics come alive - ignition - wipers - indicators et cetera.
In the second position it makes - should make - the starter motor run - activate a big high-current relay (you might hear it click) which makes the starter turn over
When the key is turned off the ignition circuit is cut and the engine stops.
It sounds to me as if your van has a starter motor problem - motor itself or the relay that makes it turn - possibly the wire that runs to the starter relay - a much cheaper fix.
Get yourself close to the starter motor - have somebody operate the switch - listen for the click of the relay - check out the thin wire that operates the relay - has it fallen off?
I know very little about motor vehicles so don't bank on my advice.
Good luck...
Jeremy Clarkson
September 2014