Starting the PC for the first time

If this computer is self build There is a switch to turn the computer on above or on top of the chassis. Then install an OS (Windows , Linux)and when installed, the OS should load. The best way in that case is uses another computer , laptop or tablet to download the OS then burn the file to a USB key and boot up the computer with inserted key. to set the os to usb key download rufus for example and that app can place any downloaded OS copy to the USB stick and make it bootable.

But wait: Does he wants UEFI boot or the old style boot ,in case of UEFI he should go first to the bios and turn of Legacy support . Where that stands look in the main board manual and then install the OS .

Once the OS has started then it's time for drivers,The most important driver is the network driver, this again has to be downloaded from another computer from the asrock server for that specific board.
When the computer can get on the network then he can download chipset drivers, USB3 drivers and video drivers.

If the computer is not turning on when pressing the start button then something is wrong in the setup, for instance power switch not correctly connected. Modern computer have also a reset switch press also on the reset switch , if the computer runs then reset and power are switched.

If the computer can not reach the BIOS the board will have a led number presentation if it halts then strip the computer main board + 1 ram stick and start the computer then , does it start and that easy to check press the power switch and the system turns off immediately. Install the video card. start again and see if You have video so can see the BIOS starting then add ram and boot up again so to pin down a problem. If the bios can't se hard disk but usual ssd in a m2 slot check on Asrock for new bios and copy on usb stick formatted as fat32. start tap several times on the F2 to access the bios and udate the bios, see also the main board manual.