Understanding startup tones

One tone repeating every five seconds

This means there’s no RAM installed in the Mac, so install some! Three successive tones and a five second pause, repeating on a loop

This means the RAM has failed an integrity check; replace it.

One long tone while holding the power button

An EFI ROM update is in progress on pre-2012 Macs. Three long tones, three short tones, and then three more long tones

Mac is in EFI ROM recovery mode.