Today I, out of curiosity, disconnected an external floppy drive from a running Toshiba 400CDT and a second later the laptop powered off and never powered on back again. Now it just blinks with the orange AC led when the power button is pressed. Service manual says it means that "AC power cord’s voltage supply is abnormal or the power supply is not functioning properly". Voltage has obviously nothing to do here as the led blinks even when the AC power cord is disconnected. So I have no idea what it means.

I observed similar blinking behavior some minutes before the accident. Then I disconnected the power cord and the battery and it helped. Now nothing helps, the laptop just doesn't power on anymore.

So I wonder was it me who killed the motherboard by disconnecting the external floppy drive from a powered on system, or the laptop was about to die anyway. I can't find any User guide for this model online to learn what was the vendor recommendations for connecting/disconnecting of the external floppy drive, so any information on this will be appreciated.

Let me know if you hotplugged an external floopy drive to your Toshiba (T21xxCx or T4xxCDT) without causing any damage.

I am going to try another PSU with this motherboard to see if it's a PSU problem. Does it make any sense or is it definitely the motherboard who died?