When powering on, a refurbished Lenovo Thinkpad T540p (which worked for a few months without any problems) shows "0190: Critical low-battery error".
Although the Thinkpad splash screen says to press Enter to see the BIOS settings, that doesn't work. The system immediately shuts down.
The manual says for this error:
Solution: The computer turns off, because the battery is low. Connect the ac power adapter to the computer and charge the battery, or replace the battery with a fully charged one.
Unfortunately the laptop won't boot when plugged into AC either. And I've also tried removing the battery and just using AC, and it won't boot at all (and doesn't even show the error).
I've tried unplugging the coin cell CMOS battery and plugging it back in (since I read on forums that resetting settings in this way might help).
The only effect was that now I also see a new error upon boot:
0251 : System CMOS Checksum bad – Default configuration used. Real Time Clock Error – Check Date and Time settings.
I've also tried replacing the main battery and also the charger. Neither helped.
A friend uses her Thinkpad T540p plugged into the wall without a battery.
The fact that mine can't do this (boot up while relying on AC power from the wall, leaving the main battery removed) implies to me that the problem is neither the main battery nor the charger nor the coin cell battery but instead is the wiring between the AC charger port and the rest of the system.
That is, even when a known "good" charger is plugged into the power port, the power isn't flowing through to the system or to charging a dead battery.
What should the next step of my diagnosis (and fix) be?
It's confusing to me that the computer worked fine for months, and now that the warranty is expired, it won't charge or boot up, even though I can't think of any event that would have caused this problem.