fuel filter or battery?

Hi my name is beth and I recently purchased a 93' geo metro. The man I bought it from said that it ran fine before he put it into storage in november but after the removel of some stereo equipment it wouldn't start.
when the battery ischarged, it will get a spark but still wont start
all plugs and wires have been changed out fresh oil has been added
as well as dry gas (originally it was thought to have water in the tank) also the fuel lines were flushed all that is left is to change the fuel filter
but the battery seems to drain fast ....... overnight ,infact.
even when it is charged or hooked up to a charger unit it wont start.
could there be a loose or ungrounded wire left somewhere that is draining the battery or might the battery just be bad and could the battery problem be the sole reason for the car not starting?

try jumper cables or another battery. does car crank over but won't start or doesn't do anything?