iPhone 8 suddenly can't switch on for the first time, tried many times hard reset wouldn't work

Hello SKGD203,

If you've tried all of the other steps, I guess that that battery could be completely dead. See this:

If your iPhone, iPad, or iPod touch won‘t charge

Note: you've tried connecting to your computer, correct? See this link for details:

If your iPhone, iPad, or iPod touch won‘t turn on or is frozen

If no help, your only other alternative is to have it checked:

Apple - Find Locations

Good luck.

Hello,

Start here:

If your iPhone, iPad, or iPod touch won‘t turn on or is frozen

Note: you may have to connect it to your computer as indicated. See this for more detail:

If your computer doesn't recognize your iPhone, iPad, or iPod

Good luck.