No ground to battery

[Tampa 735il]

I have continuity to the positive post of the battery to the under hood jumper post. I do not have return continuity to the ground post of the battery. Car has been out of servise for three years and started. Next day nothing no dash lamps etc. Seems like the battry ground is lifted any hints?

[91 bird]

could try running a wire from the neg terminal to the body and see if you get anything. if you do, then i would get a new ground cable. also check to make sure the cables are tight at each end, and battery is fully charged.