@roozbehd check your power supply first
[image|3206318]
After that check your DC in Jack. Make sure there is no corrosion, damaged pins or debris in the jack. You can always use a few puffs of compressed air to clean it. If your power supply and your jack are okay, it'll be time to open your Lenovo up and check the DC in jack to ensure that it.
a. receives power from the power supply,
b. that everything is properly connected.
Now is also a good time to check the battery for any swelling etc. You should consider changing it since there is a possibility that his is/was one of the issues.
Use this [document|32954] to work on your Yoga