I hope it isn't this for your pride's sake, but I have almost paniced over
this one and I'm a mechanic!  Did you double check that your van was in PARK?
 The auto tranny Vanagons will not start unless in Park or Neutral.

If you van is in Park and still will not start:
The other thing that I would suspect would be the neutral safety switch in
the automatic transmission.  I would hold the key in the start position and
wiggle your autotranny gear lever a little.  It should start right up if this
is the problem.  You could also go through all the gears and return it to
Park and try it.
Had this happen a few times in my van ('91 Carat) with the automatic and then
not happen again for 6 months.
Hope this helps you.
Ken Wilford
Van-Again
John 3:16