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.