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HP Z420 4 Beep on boot, red light flashing BUT works if CMOS cleared

By zabits ·
Tags: Hardware
Hi there,

My workstation HP Z420 is dual boot MacOS and Ubuntu. I'm having problems booting it up. It beeps 4 times, once per second, pause for 2 seconds and repeat.

I can make it boot if I remove CMOS battery and put it back in after at least 30 mins but this is temporary as if the workstation restarts then the same problem persists.

BIOS settings need to be ACHI in order for MacOS to function but since I take out the CMOS battery the bios resets to default which is RAID+ACHI. If I change the BIOS then the workstation restarts and same problem persists.

I have reseated the RAM and other peripherals but the problem still persists.

Do you think theres a problem with my PSU or motherboard? Do you have any tips?

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