Brad wrote

My brother gave me his "dead" Compaq Armada 4210T laptop to repair.
I normally service TVs and other stuff. With fully charged battery,
absolutely nothing (no hard disk spin or floppy disk drive noise
(with a boot floppy), no "beeps" or lights) happens when you turn it
on, but with the room totally quite, if I put a floppy disk in the
drive, I can hear a faint noise when I turn on the power (but floppy
drive doesn't run). If I remove the floppy disk, it isn't there.

One other thing that happens, even when using the external power
(plugged into AC), 4 of five LEDs (power, caps lock, scroll lock,
numb lock) light up (the battery charging LED is off). You can't
turn it "off" to make the LEDs go off by pressing or holding down the
power button. However, if I hold down the Ctrl key, then press the
power button, the LEDs go off and I hear a faint "tick"

I opened the unit and found a tiny 5A fuse, but that tested
good (not open). I examined circuits for bad solder joints.
Also checked for loose connections of any kind.

What happens with no battery at all ? The battery can
end up so stuffed that it stops the system powering up.