Restore failure could not validate source - error 254

Original install restore media, that would be able to format the hard drive, such

as Leopard 10.5 or Tiger 10.4 on DVD is one way that if you had those discs to

use, you'd be able to reformat the hard drive if the optical drive worked.

A previously installed newer Lion 10.7.5 or later, would give the device a Recovery

partition; that until the hard drive were erased totally could allow startup from there.

• About macOS Recovery - Apple Support

• How to reinstall macOS - Apple Support

Once that's gone, to try & use internet Recovery (start up in macOS recovery) and

see if the MacBook could sustain a new installation. ~ This may take time, online.

There are options, so read details; and consider their intent before proceeding

If you totally erased the hard drive, the need to access macOS Recovery and use its

utilities to try & reinstall; forgoing that, reformat the hard drive. Depending on the unit

could be the hard disk drive itself may have failed.

There was a way to create a bootable installer; better done with the installer prior to

using it (because it goes to Apple download servers) to get the whole file. That can

be rather huge; and of late, the only thing most said they got was the initial installer.

Difference? A 'install starter' few hundred MB in size; or full content of many GBs file.

Not sure if the free utility [ DiskMaker X ] could be of help, especially at this time.

Sorry to not offer much to assist at this late of time. Nearly 1:30AM here. {..Zzzz..}