2005 Isuzu ascender 4.2 computer module location so I can replace it.

You were "told" the computer 'may' be the problem .. That isn't much to base your diagnosis on! First off - that is the 'least likely' suspect for a no vehicle power condition .. I could post a list of the many possibilities, however that is not beneficial as this issue requires *hands-on* testing by knowledgeable automobile troubleshooting personnel.. You'll be wasting money to do otherwise!