1991 Cadillac Brougham cadillac repair

i own a 1991 cadillac brougham.its been starting and running perfectly fine!.i drove it to the store,then back home.then i headed back out again.i disarmed the car alarm,got inside,put the key in the ignition.the radio and dash lights all came on as normal,but when i put the key in the "start" position,i had NO power,i turned the key back into the "off" position and back into "start",but nothing happened,not even a click.no lights,no radio or no engine start..i hooked up jumper cables,but the car wouldnt start.i let the battery charge for about 10 minutes.i opened the car door and the interior door lights were on,but quickly went off as i tried starting the car again,which made a slight click but never started,then i no longer had any interior door lights either..someone told me it was the starter,but im thinking its the battery,but i dont know.the battery is "allstate" and its about two years old..can someone help me solve this problem? Thanks