iPhone will not turn on

It isn’t quite as simple as holding all the buttons, there is a specific way to do it. See this for some help.

If your iPhone won't turn on or is frozen - Apple Support

There is a link at the end of the support article that you can click on in order to contact Apple support if needed.

If your iPhone won't turn on or is frozen - Apple Support

It may be time to make an appointment at the nearest Apple Store for an evaluation and explanation of your options.

https://www.apple.com/retail/