You see nothing on either monitor even during the very early stages of the boot process (before any boot drive is even touched) does look like it could be a bad motherboard - assuming the power supply is working properly. A spinning drive motor and lit LED does suggest the notebook is getting power though if me, because I have a universal notebook supply handy I would try it just to be sure. But frankly, I think that is just reaching for hope.
If you saw anything during the early boot process, I would suggest trying to get into the BIOS and change the order of your boot drives and try to boot to a DVD or flash drive, but you cannot even do that.
You also already tried booting without the battery with the same results so that suggest it is not a shorted battery drawing too much current. Booting without a battery also takes much of the demands off the charger, so again, it would "appear" your charger is working fine. Many notebooks have a fuse or similar over-current device, but if blown/tripped, you typically don't see any indication of life - that is, no spinning drives or any LEDs. So I am afraid I don't know what more to suggest but to take it to a shop and let them open it up and maybe find something simple. That said, you said this was an "old" notebook so not sure how cost effective it would be to have a pro look at it as they would like charge you 1 hour of labor just to have a peek.
If you are adventurous, you could open it up yourself (take battery out first and unplug charger) and look for loose cables, sniff for any burning smells, or other telltale signs of damage. Make sure the fan spins freely and is clean of heat trapping dust. Note a CPU fan that does not spin could halt a system almost immediately.
Sorry.