1995 Chevy Beretta Starting Problem

Hey guys, I killed my Beretta and now it doesn't want to start. It ran fine all the way home from work. Went to the store & come home & it won't start. Hooked up the battery charger & the battery is down at 75%. Jumped it off another car & it cranked right up. Took it around the block & it was running rough. Got back home & it wouldn't start again. Added water to the battery cause it was low. It still won't crank. The dash battery light stays on while it's idling, but when you take off it goes out like it's trying to charge. Please help me get this thing going. It's all I have to get me back n forth to work. I can't loose my job it's the only support that I have. Please please tell me what I can do. Shawn