Mac Mini OS High Sierra will not boot.

The following table lists the new tones and their meaning:

Tone(s) Description

1 tone, a 5-second pause, repeat No RAM installed

3 successive tones, a 5-second pause, 3 successive tones RAM does not pass data integrity check

1 long tone when holding down the power button Firmware upgrade in process. See About firmware updates for Intel-based Macs for more details.

3 long tones, 3 short tones, 3 long tones Firmware restoration from CD in process. See About the Firmware Restoration CD (Intel-based Macs) for more details.

If your Mac beeps during startup - Apple Support

Do the beeps match any at > If your Mac beeps during startup - Apple Support

If so, then that article should give you a clue as to what is wrong.