Question PC won't turn on with Case Power Switch

Feb 18, 2021
I wonder if someone can help me with my query.
System Spec –
- i7-10700, 16GB RAM, RTX 2060 Super, 512HB SSD + 2TB HDD, MB – Asus Prime B460 PLUS

It’s a fairly new system, I’ve only had it since Sept 2020.

I am having trouble turning my PC on, it doesn’t turn on when I press the power button (on top of the case) & will only power on via the PSU On/Off switch (Intermittently).
This only started when I changed the Fast Boot option.
I’ve tried changing the power & sleep settings to default, disabled Fast Boot option in the BIOS, also tried removing the motherboard battery & reinstalling it, still no luck.
Updated BIOS to the latest version, updated windows 10 too, but still the same issue.
Appreciate any help, thanks.