2000 Other Kia Models no electrical to start car

my mother inlaw has a 2000 kia sephia , the car was running great a couple months ago , but sits for periods of time without use. a couple weeks ago i hear she cant start it , there's no dome light or anything else , so we charge the battery and install, dome light comes on so and the seems to get some electric power, tighten the cables , then i hear a tic...tic...tic kinda noise ,my from below the fuse box area , and them the car loses all electric power , almost like the battery went dead instantly , no juice at all , not even a dome light, check the battery, says fully charged, both fuse boxes are ok , any ideas what happened... thank you, Dave