Dead?/shorted Battery

From: ernio37

My Acer 5100-3123 notebook battery suddenly went dead. I tried to start my PC with battery in and external power on but no go. I then tried just starting on battery, no go. then I tried with battery out and external power on and it booted but wouldn't stay on. after much research I found the HDD was damaged at same time battery seemed to be shorting out but was dead. It showed no charging activity and would not charge. I tried restoring from backup but wouldn't work. Then i tried installing XP OS wouldn't work. then I replaced HDD and installed Vista on that and it worked for a short time on external power only but then gradually I had to fuss longer and longer to get it going. I finally found I could boot up every ti me using Spotmau PowerSuite. I then installed a new battery and saw it was 78% charged and was charging. I went away and returned a short time later and found the PC SHUT OFF AND COULD not restart it until I removed the new battery and started on external power. I also still have the problem with the boot issue. Does anyone have any idea what could be wrong? Is it a defective Mother Board or a defective new battery or the bios, or is there a short circuit in the computer? I'm at my wits end with this thing, and it's only my stubborn nature that persists in trying to repair this piece of junk. PLEASE HELP IF YOU CAN THANKS, ERNIO37