Marebella wrote:
Disk utility showed no problems with Macintosh HD or disc image volume (OS X Base System).
The "OS X Base System" is the virtual volume for the macOS installer. Just ignore it.
It finally seemed like it was going to install OS but when prompted to select where to install X Yosemite, no disk appeared and could not advance beyond that point.
The reason why the Yosemite installer doesn't see a valid destination is because the Big Sur boot volume is incompatible. You will need to partition & format the whole physical drive using the instructions in this article:
https://eshop.macsales.com/tech_center/formatting/Mac_Formatting_6-10_R3.pdf
However, before you try to do this I would suggest trying to boot into Internet Recovery Mode using Command + Option + R to attempt to access the online macOS Big Sur installer. Unfortunately some Macs may still only boot to the online installer for the OS which originally shipped with the Mac from the factory regardless of the keys used. If you can access the online Big Sur installer, then use Disk Utility to erase the whole physical SSD as GUID partition and APFS (top option). Then quit Disk Utility and select the "Install macOS Big Sur" option.
Keep in mind erasing the SSD and partitioning & formatting the SSD will destroy all data on it.
Do you have a backup?
If no backup, Did you have Filevault enabled on this SSD? If so and you cannot successfully reset the login password, then the only way forward is to erase the whole SSD.
If Filevault was not enabled on this laptop and you don't have a backup, then you can retrieve the data from the SSD by booting from an external macOS boot drive. If you don't have an external macOS boot drive, then you can install macOS to an external USB3 drive if you have an extra drive that can be erased. Boot from the external macOS drive and try accessing the documents to move them to another location. You need a macOS 10.13+ boot drive, but it would be best if Big Sur was on it as it makes accessing the internal drive much easier....you may need more instructions to access the data if you reach that point. Just make sure when installing macOS that you choose the external drive as the destination. Or if you have access to another Mac, then you can try to recover the data by putting your "broken" laptop into Target Disk Mode.
