My lenovo t400 won't open. the battery and other lights flashed then nothing happens

i found these places for you its only info but it may help you out.
https://forums.lenovo.com/t5/ThinkPad-T400-T500-and-newer-T/T420s-No-power-blinking-power-Led-won-t-boot/td-p/684845
or
Computer Won Turn On Only the Light

try changing the keyboard because switch is on keyboard and use adapter to plug and test

Just because you charged the battery it doesn't mean it is any good. Modern sealed batteries fail; just as you described, fine one moment and then nothing, they go open internally.

A less frequent situation that can happen in a laptop resulting in it not booting up is a damaged USB port. If the pins are touching the system will not start up. You can fix this problem by using a small flat blade screw driver, tweezers or micro needle nose pliers to carefully separate and reform the contacts so they do not touch.
This is not a permanent fix because the USB port will become unusable. To fully fix it would require you to replace the system board, which may or may not be covered under your warrenty.

bad battery

I have rhe issue can someone help me please

if you battery is working and you have continuous A/C power. laptop has a hardware failure :(

Maybe you need a new battery for your laptop Thinkpad t400; you can buy a 6-cell battery from http://www.aubatteries.com.au/laptop-batteries/lenovo-thinkpad-t400-series.htm
http://www.all-batteries.co.uk/notebook-batteries/lenovo-thinkpad-t400-series.htm
http://www.notebook-battery.org/notebook-batteries/lenovo-thinkpad-t400-series.htm

I got the same problem. Have u resolved the it? If so, please send a message to: [email protected]

Hi guest, try to turn off the pc by using the power button. Then remove the cables and battery on the laptop. Then push & hold the power button for 5 seconds. Reinsert the cables and battery then turn on the pc.

Check if you will be able to shut down your pc using the operating system..