iMac (2009) fails to install El Capitan after reset

Hello all,

I was hoping for a little assistance with a recent problem I've been having regarding the installation of software after a system reboot.

I recently reset an old iMac, because my Dad recently passed away and I wanted to clear any of his saved details before giving the computer to my neighbour son.

Whilst it's an older machine, it was working perfectly prior to me doing the reset.

But sadly, now having done the reset, the software (El Capitan) doesn't seem to want to re-install.

The errors that display are...

"The server gave an error during download: 403 Forbidden" and "An unexpected error occurred while signing in: plist parsing error".

El Capitan is the most up-to-date software I'm able to install on this Mac. Additionally, I also tried to install the original software which came with the iMac (Snow Leopard) as I have it on a disk, but sadly it seems like the disk can't be read.

I would love to know if anyone has any ideas on how I can solve this issue. Whilst I'm no longer using the machine, I had already promised it to my neighbour's child, so I would love to get it working again if possible.

I did have a conversation with the Mac team and they suggested I posted in here, as there are more legacy users in the forums than there are on their current support team. She suggested that someone might be able to advise on how to create a bootable installer—but I'm also open to other ideas if there are other potential solutions.

Any help or advice would be hugely appreciated.

• iMac Info: The Mac is a 2009 iMac (which originally came with the Snow Leopard operating system) and the most up-to-date software it can run is OS X El Capitan.

Many thanks,

Greg