With the charger disconnected I would disassemble and take the battery out. Then press the power button to discharge any power in the system. Go off and have a cup of tea and then install the battery again. Plug in the charger and wait about 30 minutes. Unplug the charger and then press the power button. Does the laptop turn on?
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Did you double check that all cables, etc. were reconnected correctly before reassembling? Troubleshooting often is about finding the simple, obvious solution. We humans tend to think too complicately. Of that simple solution may take a bit of work to find!
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With the charger disconnected I would disassemble, check as above. If all looks good then take the battery out. Remember to press the power button to discharge any power left in the system. Go off and have a cup of tea and then reinstall the battery. Plug in the charger and wait about 30 minutes. Unplug the charger and then press the power button. Does the laptop turn on?
With the charger disconnected I would disassemble and take the battery out. Then press the power button to discharge any power in the system. Go off and have a cup of tea and then install the battery again. Plug in the charger and wait about 30 minutes. Unplug the charger and then press the power button. Does the laptop turn on?
If not replace the battery.