You could use a voltmeter to check the output of the charging brick. The required voltage output is printed on the bottom of the charging brick.
While the laptop is in use, feel the area around the DC-IN jack (jack that accepts the charging brick cord). If this area is hot to the touch, you found your problem, the DC-IN jack.
Part number: 90NB06F1-R10030 or 90NB06F1-R10080 or 90NB06M1-R10030 (any would work) Cost: $25-$30
If the DC-IN jack area is rather cool, then you have a defective motherboard. Part number of the motherboard is on a green label with black lettering. The motherboard must be removed to see this label. Use this part number to order/replace your existing motherboard.
I would strongly suggest you replace your battery while replacing the motherboard.