Hi
Here’s the [http://h10032.www1.hp.com/ctg/Manual/c03694820.pdf|maintenance and service guide] for the laptop, taken from this [https://support.hp.com/us-en/product/hp-envy-m6-1100-notebook-pc-series/5296045/model/5312259/manuals|webpage].
Go to p.69 to view the necessary pre-requisite steps and then the procedure to remove /replace the power button board.
Once you have disconnected the board you should be able to work out how to test if the button contacts are OK by using an Ohmmeter to test for continuity when the button is operated.
If the button is faulty it may be easier to simply replace the board. Just search for ''686917-001'', to get results for suppliers that suit you.)