Ford Repair: 93 Explorer, quick zap, cable insulation

Question
My Explorer won't turn over, it just sounds as if there is one quick zap or spark when I turn the key to start it.  The battery reads that it is fine but the cables are both old, cracked and corroded.  At first, the negative cable was very loose and when I tightened it the Explorer still didn't start.  I tried again later, and it started.  I drove to my destinations turning it off at each one.  The next day I went to drive my Explorer and it wouldn't even turn over.  How do I know if it's just the cables that need replacing or could it be something else?  Also, I would like to change the cables on my own, how difficult of a job is this for someone who has never done this before but is always willing to try anything at least once?
Thank you in advance for your help!

Answer
I think you answered your own question, if there is corrosion that is a big problem. If this gets inside the cable insulation it can create a lot of trouble. It sounds Basically it amounts to check each circuit between contact points, say at the battery negative post and the engine ground. Another thing to check, under the battery on these early Explorers some would leak acid onto the harness and cables and cause problems.

The battery and all related connections have to be clean, free of corrosion, and tight for things to operate properly.