HP ProBook 6560b won't turn on, no LED flashing

[djordjejovanovi]

Probook 6560b stopped responding after i disassembled it and placed a hard drive caddy with a 500GB SATA3 hard drive, at first it was visible and worked, after a shutdown the computer stopped responding. No visible signs of damage to the motherboard or any other components when disassembled.
No signs of life, LEDs stay off, the screen is completely blank, no sound from the motherboard or hard drive.
I've attempted to disassemble it and reseat the RAM and CPU, to no avail. I've also tried to discharge static (and many other fixes i found online) to no avail.
All i've managed to find is that the battery power port (measured with a multimeter set to 20V DC) fluctuates from ~7-8V to 1.8V, the AC adapter seems perfectly fine with 19.3V.

[Huffer]

If it booted up after installing the hard drive then that was not the cause of the issue. That is a much older laptop and I am going to suggest it just met its end. The fluctuating battery power port indicates a motherboard failure. Does it perhaps show any signs of life if you remove the battery and AC plug and hold down the power button 30 seconds and then plug in AC adapter but not battery and try to power it on ? It seems you likely already tried that. 

[djordjejovanovi]

I did try powering it on without the battery, no signs of life whatsoever.

I have another ProBook 6560b and interchanging their power components didn't produce any issues.

All i can say is that the only plausible cause of failure was that i maybe damaged a component in the dvd drive section by putting the hdd caddy in there? It would certainly explain the voltage issue.

Also, about the battery power port (the 6 or 7 card edge connectors the battery uses to charge) every single time i measured them (at 20V on a multimeter) they would start out at 6-8V and start dropping slowly, until they would reach 1.8V and stop moving. I also attempted moving up the connector, to no avail. It still produces the same results.

If the computer did meet it's end i'll probably attempt to replace the mobo and the rest of it's components i find to be faulty.

[Huffer]

Yes you can certainly find a motherboard for it for a pretty reasonable price. Let me know if you need any help with that. 

[djordjejovanovi]

Which site would you suggest for looking for a motherboard? I haven't really bought hardware like this before.

[Huffer · Accepted solution]

Here is the Service Manual:

Manual 

There are several system boards listed. You need to find one that will accept your processor, memory and other peripherals. Get the HP Part number of a board you can use and search eBay. eBay UK, France or Germany ought to have one available. 

This one works with Quad Core processors (see pages 27 and 28):

QM67 with WWAN
For use in all countries and regions except for Russia and the People's Republic of
China
646964-001

QM67 with WWAN
For use in all countries and regions except for Russia and the People's Republic of
China
646965-001

646965-001 HP ProBook 6560B Motherboard 8560P Laptop | eBay

You just need to search until you find one for a better price. Also I am not sure if maybe yours came out of Russia, which would be a different board. Good luck and please accept as solution if the info I have given has helped.