I don't think paying cash for a van affects your credit. If anything it would hurt it, just like having credit cards and not using them.
Contact the three credit agencies (Equifax, et al) directly and have them remove whatever block you put on it. It was probably an anti-theft thing.
They'll probably send you recent copies of your credit report. Go over it and make sure any account that is closed says "Closed By Consumer" (you'll have to write to each store and tell them to report it that way). Make sure all the info is accurate. This will help you start getting your credit rebuilt.
Diane
The business writer who helps people grow their small business
http://www.BouncePublishing.com