Dell Latitude D620 Will Not Post/Boot/Start! Orange solid battery light when power is pressed. Help Please!?

I have a Dell Latitude D620 Laptop. About a month ago, it was given to me by my father and he said it just needs rebuilt. He’s used it for a while and it’s never had any issues prior. The battery in it was indeed bad, but it worked fine while plugged in. I rebuilt the operating system, installed all the drivers, rebooted several times during the process. Once i was finished, i had a spare D620 battery laying around that i wasn't sure was good or not. I decided to take out the known bad one, put in this other one and see if its good. Upon swapping, i plugged in the power, and nothing happened when i hit the power button. No lights, nothing. So I took it out, put in the known bad battery, and hit power again.... now nothing comes on even with the battery that just allowed it to boot 2 minutes prior... I have reseated the ram, tried with no battery, different charger and still nothing. It sat for about a month now as I was frustrated with it. Today, I found a battery module for the D620 that sits in the CD-ROM bay. I installed it, and now when plugged in and I hit the power button, the battery light came on as orange, not flashing, just solid. When I let go of the power button it goes off. As long as the power button is held in, it stays on. Any idea’s what is wrong? I can’t seem to find any clues