Chevrolet Repair: 1997 chevrolet astro van, chevrolet astro van, little fuse

Question
97 astro van/148,000 miles. Will not start, no dash lights. I replaced the 40a fuse in the engine compartment only to have it blow the moment I turned the key. The "check engine" is on...so I rented a code reader from an auto parts store. I had  
no problems before I plugged the reader in. Could there be a short somewhere around the reader plug-in receptacle. Also, the van had sat idle for about 3 months, just the occasional start up to keep the battery charged. Thank you very much for any assistance. James

Answer
Hey,

 It might just be coincidental that the fuse blows now.  Which fuse is it and I will try and isolate what circuits are involved?  Check the little fuse panel by the battery and make sure there is no cracks in the base making wires touch.  

wayne