I have an old Dell Inspiron 1525 that won't boot up but both battery charging blue light and power on blue light are on. The battery wouldn't charge so I bought a new battery and new adapter. Worked for a few months then stopped charging. Computer said BIOS update needed but couldn't charge battery enough to update BIOS. So I replaced the "Coin Battery" on the motherboard to see if that would fix it.It didn't.
Now, the hard disk light flashes once (blue) then goes off. Prior to replacing "Coin Battery" the computer would attempt to boot and the big, blue "DELL" logo would pop up on the screen. Now the screen stays black.