When you say the battery "seems to be ok," have you checked it other than
turning on the lights, etc.? These accessories don't draw nearly the charge
it takes to run the starter, so they aren't a real indicator of whether or
not the battery is adequately charged.

Here's a plan. Take the battery back to where you bought it, and have it
fully tested/recharged. Should be free. Then reinstall it and see if the van
starts.

If it does, you have a current drain on the battery which a test with a
multimeter should show. Find this current drain and fix. I'd start with the
stereo, but that's just a guess.

If the recharged battery still gives the same results, check the ground wire
to the frame, and all other connections that go to the starter. Only after
doing that should you suspect the starter, the solenoid, etc.

My guess is that you either inadvertently drained the battery overnight or
there's a bad connection, maybe even the connection at the battery itself.

It's really not such a hard problem to fix. Don't lose hope.

Geza