My Toshiba l645d won't turn on without being plugged in when turned on screen stays black fan starts but run only for a moment
Ok, is there an indicator showing that the PC is on? If so, does it stay on when you turn on your PC when it's not plugged in.
If it remains on while you turn on but there's nothing other than the indicator, then get your PC fixed. If it doesn't remain on, test this. Leave your PC on with the battery and it plugged in, then try to unplug it while the PC is on.
If your PC still works after the plug is removed, then it's an issue that I don't know about. If your PC doesn't work, it could be a dead battery.