What should I do if my system doesn't boot after changing BIOS settings?
If the system fails to boot after changing BIOS settings, try to clear the CMOS and reset the motherboard to default values. This can be done by short-circuiting the Clear RTC RAM jumper (CLRTC) for about 5-10 seconds while the power is disconnected, then reconnecting power.
From the official ASUS Asus Prime Z390 A Motherboard User manual, page 64
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