Issues post upgrading to elcapitan final version

Downloading Mountain Lion is hardly a post El Capitan issue. Exactly what is your problem. Please try stating it clearly.

As you can do a normal Internet Recovery here's how it should be done. This should work because it is going to erase the drive first:

Install OS X Using Internet Recovery

The following procedure will remove everything from the hard drive. Backup if you can.

Boot to the Internet Recovery HD:

Restart the computer and after the chime press and hold down the COMMAND-OPTION- R keys until a globe appears on the screen. Wait patiently - 15-20 minutes - until the Recovery main menu appears.

Partition and Format the hard drive:

1. Select Disk Utility from the main menu and click on the Continue button.
2. After DU loads select your newly installed hard drive (this is the out-dented entry with the mfgr.'s ID and size) from the left side list. Click on the Partition tab in the DU main window.
3. Under the Volume Scheme heading set the number of partitions from the drop down menu to one. Click on the Options button, set the partition scheme to GUID then click on the OK button. Set the format type to Mac OS Extended (Journaled.) Click on the Partition button and wait until the process has completed. Quit DU and return to the main menu.

Reinstall OS X: Select Reinstall OS X and click on the Install button. Be sure to select the correct drive to use if you have more than one.

Note: You will need an active Internet connection. I suggest using Ethernet if possible because it is three times faster than wireless.

This should restore the version of OS X originally pre-installed on the computer.

I'm getting the same error message on my MacBook. I tried doing a cold boot but get the same results. Its basically a paper weight right now. Should I use the Kappy suggestion?

Yes, please do as I suggested.

I hit the APPLY tab, the othe tab was REVERT. Your instructions did not mention to do so but I just assumed it was necessary. When I did I got an error message "PARTITION FAILED: Couldn't unmount disk." What now?

Did you boot from the Network Recovery or did you boot from your local Recovery HD? If the former, then you can try this with the Utilities Menu visible:

From the Utilities menu in the screen menubar select Terminal. When the Terminal opens enter this at the prompt:

diskutil unmountDisk force /dev/disk0

Press RETURN. If no error occurs then quit Terminal. Select Disk Utility from the main menu and click on the Continue button. Now, retry the process. At the end you do click on the Apply button. The Partition button is no longer displayed.

I don't know. Its been so long LOL. Right now I am looking at Disk Utility with a window that on the left column says 250.06 GB Fijitsu... UNder that on an indented line siys MacIntosh HD. Down lower it says disk1 and OSX Base System on the indented line. If I highlight the 250... I see tabs of First Aid, Erase, Partition, RAID and Restore. If I hit the Mac HD the Partition tab goes away. If I hit the OS X Base line First Aid, Erase, and Restore tabs appear. I ran First aid check on the disk and it shows ok.

Let's review just to be sure:

You need to connect to your Ethernet port if possible. Wi-Fi is much slower and less reliable. You will be booting from the Network installer, not your local one:

Install OS X Using Internet Recovery

Shut down the computer. Wait two minutes.

Boot to the Network Recovery Server:

Restart the computer and after the chime press and hold down the COMMAND-OPTION- R keys until a globe appears on the screen. Wait patiently - 15-20 minutes - until the Recovery Utilities main menu appears.

Partition and Format the hard drive:

1. Select Disk Utility from the main menu and click on the Continue button.
2. After DU loads select your newly installed hard drive (this is the out-dented entry with the mfgr.'s ID and size) from the left side list. Click on the Partition tab in the DU main window.
3. Under the Volume Scheme heading set the number of partitions from the drop down menu to one. Click on the Options button, set the partition scheme to GUID then click on the OK button. Set the format type to Mac OS Extended (Journaled.) Click on the Apply button and wait until the process has completed. Quit DU and return to the main menu.

Reinstall OS X: Select Reinstall OS X and click on the Install button. Be sure to select the correct drive to use if you have more than one.

Note: You will need an active Internet connection. I suggest using Ethernet if possible because it is three times faster than wireless.

This should restore the version of OS X originally pre-installed on the computer.

Same as before. I followed what you said to the letter unless there is some confusion as to "Network Installer". Can we use the erase or restore tab? As stated earlier I see a OS X Base System under out dented disk 1. I dont know what this is but it appears to be a Recovery HD from a folder labeled "com.apple.recovery.boot"

So, when you open Disk Utility you do not see your hard drive or SSD in the Disk Utility list of devices? If that is the caae, then your drive has failed. You cannot repair the drive if it does not appear in Disk Utility. If there were one, then it may appear like this:

Above you can see the out-dented entry is the physical drive ID under which is one indented entry, Macintosh HD Backup. The ghosted entry is normally invisible.

If you don't see something like the above then the disk drive is shot.

I see the HD (250,06 GB ...). But I can't partition it. The PARTITION LAYOUT shows "Current" but I cannot change it to 1. Didn't see what would happen with 2 or more.

If you click in the box on the right, then select the number of partitions from the dropdown menu above it.

I tried that. It won't let me partition

I think your drive may have failed, then.