HELP! No power...?

mine had done this too way way back when i first got it..anyways seems way too obvious but the guy that sold it to me had thrown an old battery in it out of an onmi just to start it. the terminal post were very small being that small of a bat and although the battery terminals appeared tight, they were not b/c the post were small. i assume you have cleaned and checked them already though? so maybe start pulling fuses next...but the fact u have a COMPLETE power loss...almost has to be something very close to the battery. unless your tester is bad and its actually dead.