Hi Eric.
First of all, you need to make sure that your problem isn't with the spare battery.
If your computer starts up with the charger alone, you'll know that the battery is at fault, as was the case for me.
The only difference was that I could boot up with the charger but the battery icon showed 255% charge and as soon as I removed the charger, the tablet shut down.
For your information, I was able to check that my battery was dead using the "powercfg" system command => more information here:
https://fr.ifixit.com/R%C3%A9ponses/Affi...
In your case, you'll need to disconnect the battery from the motherboard and see if your tablet starts up again, just with the charger. To do this, you'll have to dismantle the tablet again (I feel for you and hope you haven't glued the screen back together).
You can avoid completely dismantling the motherboard and some peripherals by unscrewing just a few screws on the left side of the motherboard (with the tablet in the normal position, with the wifi antennae and webcam on top) so that you can lift it slightly and VERY CAREFULLY to insert a piece of cardboard or a playing card between the underside of the motherboard and the battery connector stuck to the bottom of the chassis.
Use a piece of cardboard the size of which covers the battery connector well and which extends slightly beyond the motherboard, but not too far, so that you can both temporarily close the tablet and easily remove the cardboard at the end of the operation.
After that, reconnect the screen and peripherals for a quick test (without putting the shields back on, or applying thermal paste to the CPU if you've removed the heat sink).
Just don't leave the tablet switched on for too long.
If the tablet reboots, you'll know it's the battery, otherwise the problem lies elsewhere and unfortunately I can't give you any more information.
I hope this helps.
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