I would start with the basics and pull the battery back out and use a Power Adapter only. Reset the PMU on it and try and boot it up and see what you get.
If it’s not chiming that’s not a good sign. Pull the RAM and see if it beeps at you 3 times. If it does then at least the logic board is functioning enough to see RAM isn’t installed. From there I would test with only 1 RAM chip and see if you can get it to chime. May have to do a PRAM reset in order to get it to chime. If you can get it to chime then you are moving in the right direction. I would disconnect the internal hard drive and optical drive and just hold Option key while booting and see if you can get to the startup manger screen. If you can Option boot and it stays on the startup manager screen without shutting off or anything odd happening then shut it back down, connect your hard drive and try to turn it back on and see if it will boot to the hard drive.