How do I solve this power problem?

Okay, I am having some issues with my IBM thinkpad t43. This is what happened:

Working fine until a week or so ago, at which point the computer randomly shut off. It did not blue screen, or show anything. It instantly black-screened, so some sort of hardware failure. Afterwards, the AC adapter did not charge the battery or the laptop alone--However, the laptop ran fine on battery power. So I figured it was an adapter issue, and accordingly bought a new adapter with the same specs as the other one. The new one does not work either. I took apart the computer and have pretty much determined that there is some issue with the power supply between the AC adapter in and the battery. Any suggestions or pointers as to what I should try troubleshooting would be very much appreciated. thank you! :)