OK, now that we have a firm idea on what you have for a system we can work through the different issues you are facing here.
The first is what drives are workable: You are limited to older SATA II (3.0 Gb/s) so we need to make sure the current drive is the correct one.
The next which you appeared to have tried to over come is Apple uses a certificate system, the OS installer needs to validate its self to the systems date held in its clock. If it is not within its window it will fail, heres a deeper explanation: [https://appleinsider.com/articles/19/10/24/if-youve-got-an-old-macos-install-image-it-will-probably-stop-working-today|If you've got an old macOS install image, it will probably stop working today].
So you either need to alter the systems date or use an updated installer!
Here’s an updated installer [https://support.apple.com/en-us/HT206886|How to upgrade to OS X El Capitan], Jump down to Step 4, make sure you click on the blue URL link “Download OS X El Capitan” to get a fresh OS installer.
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You’ll need to create a bootable OS installer drive either a FireWire or CD/DVD as this series won’t boot from USB.
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[https://www.macworld.com/article/2981585/how-to-make-a-bootable-os-x-10-11-el-capitan-installer-drive.html|How to make a bootable OS X 10.11 El Capitan installer drive]
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You’ll need to create a bootable OS installer drive either a FireWire or CD/DVD as this series won’t boot from USB [https://www.macworld.com/article/2981585/how-to-make-a-bootable-os-x-10-11-el-capitan-installer-drive.html|How to make a bootable OS X 10.11 El Capitan installer drive]
Your other option is to use a second system in Target Disk Mode following this guide: [https://computers.tutsplus.com/tutorials/understanding-the-applications-for-target-disk-mode--mac-60609|Understanding the Applications for Target Disk Mode]
OK, now that we have a firm idea on what you have for a system we can work through the different issues you are facing here.
The first is what drives are workable: You are limited to older SATA II (3.0 Gb/s) so we need to make sure the current drive is the correct one.
The next which you appeared to have tried to over come is Apple uses a certificate system, the OS installer needs to validate its self to the systems date held in its clock. If it is not within its window it will fail, heres a deeper explanation: [https://appleinsider.com/articles/19/10/24/if-youve-got-an-old-macos-install-image-it-will-probably-stop-working-today|If you've got an old macOS install image, it will probably stop working today].
So you either need to alter the systems date or use an updated installer!
Here’s an updated installer [https://support.apple.com/en-us/HT206886|How to upgrade to OS X El Capitan], Jump down to Step 4, make sure you click on the blue URL link “Download OS X El Capitan” to get a fresh OS installer.
You’ll need to create a bootable OS installer drive either a FireWire or CD/DVD as this series won’t boot from USB.
[https://www.macworld.com/article/2981585/how-to-make-a-bootable-os-x-10-11-el-capitan-installer-drive.html|How to make a bootable OS X 10.11 El Capitan installer drive]
Your other option is to use a second system in Target Disk Mode following this guide: [https://computers.tutsplus.com/tutorials/understanding-the-applications-for-target-disk-mode--mac-60609|Understanding the Applications for Target Disk Mode]