Help with FileVault

I hope this provides the detail you are looking for. I connected the MP and MBP with a Firewire 400 cord and 2-400/800 adapters and then started up the Mid 2010 MP in Target mode with the SSD  in slot 1 (the one closest to the front panel), a drive with an old OS in slot 2 and a backup drive in slot 4.  (I don’t know why I have not been able to boot the disk with the old OS on it, but I haven’t.) I opened Disk Utility on the Mid 2010 MBP (10.13.6) and saw the 3 disks in the MP listed as external and a Disk Image called InstallESD in the left hand column of Disk Utility.  The SSD was greyed out, but I was able to mount it and erase it.  I then closed Disk Utility and opened the “Install macOS High Sierra.app” file that I had earlier downloaded using instructions I found on the Forum.  I clicked “Continue” and “Agree” and then clicked “Show All Disks” and saw the three MP disks in addition to the MBP disk but the MP disks were greyed out.  When I clicked on the MP SSD drive I got the message  “You may not install to this volume because it is a Mac in target mode.”  I have ordered the “USB 3.0 to IDE/SATA Converter Adapter Kit” from eBay referred to in your earlier post. The one from Newegg would have come from China and my last order from China took 6 weeks.

I thought I posted a followup, but can't see it now. If this is a duplicate (sort of) please forgive me.

Well, my computer is now frozen and I have not been able to start it up at all.  I have tried starting it up in Safe Mode (Shift), D (Apple Hardware Test), R (Recovery),  Shift-Option-Cmd-R (Recovery of the Internet), X (Different Drive) and V (Verbose).  None of these got me anywhere.  My mac is a Mid 2010 MP with OS10.13.6 on a 1-T SSD and a 2-TB hard drive with Time Machine. I installed a new video processor so it can run Mojave. I also have a mid 2010 MBP and a 2017 MBA. Can I use Target Mode and the MBA to reformat the SSD main drive on the sick MP?

I tried a number of things and then connected the MP to the MBP using a 400 Firewire cord with two 800 adapters.  I then used Disk Utility to erase the SSD in the MP and mount it.  I was unable to download 10.13 from the App Store but found a link to a site that allowed me to download a full install copy of 10.13.  I then started the install but got the message that I couldn’t do it in Target mode.  How do I install 10.13?

I do have a drive with an older OS, 10.9 I think.  However I have been unable to startup to it by pressing the X key.  There is also curious problem with my Dell U2415 monitors.  The main monitor recently started reporting that there was “No DP Cable “ when there was a DP cable attached to the MP.  I also replaced the new video processor with the original one.

There is only one optical drive.  And yes I think I formatted it as MacOS Extended Journaled. The USB 3.0 to IDE/SATA adapter arrived, and using my MBA I loaded 10.13.6 onto the SSD with the device.  I was then able to use Startup Disk to boot the MBA using the SSD.  I then installed the SSD in the MP and tried to do a startup with just the SSD and no other drives.  I heard the chime but it would not startup, or at least the monitors indicated there was no HDMI cable attached.  I have 2 Dell U2415 monitors attached to the upgrade Sapphire video processor in the MP using HDMI cables. The monitors have 2 HDMI slots and I tried both inputs to make sure I was not plugged into the. wrong one.  I even tried reinstalling the original video processor and my old Samsung monitor using my original DVI to HDMI cable.  Once again I heard a chime, and the Samsung also indicated it did not get a signal.  This seems really strange.  Why is no signal getting to the monitors?  Could I have damaged something else.

Thanks for your help.  I don’t know of any such resource in the Windows world.  

Holding the Option key down did not light up the screen at all.  I removed the SSD and checked the formatting with the USB to IDE/SATA device and Drive Utility on my MBA.  It was APFS.  If I wanted to reformat it all over again the only choices I had were APFS, APFS (Encrypted), APFS (Case-Sensitive) and APFS (Case-Sensitive Encrypted).  I have checked and there is no Apple repair facilities anywhere near.  There is a Best Buy Geek Squad open in my town.  Is it possible that the logic board is the problem?

I found a used logic board for sale on eBay. The listing says:   Genuine 2012 Mac Pro Backplane Logic Board Motherboard A1289 Apple MPN 661-5706. eBay 169.95 + 23.80 preowned Seller Notes:  “Genuine Apple   parts, fully tested, in excellent condition, fully updated firmware, and boot ROM 144.0.0.0,.0.”  I watched a YouTube video describing the replacement and believe it would not be a problem.

Yes. The SSD boots the MBP using the USB to SATA adapter and Startup Disk. So the SSD is good and may not have been the problem before. The MP worked fine for a few days after the FileVault fiasco. Then it froze and I had to do a forced shutdown using the power switch.

I can't answer that. I don't know. I just checked the 3 hard drives I took out and they were all Mac OS Extended (Journaled). I reformatted the SSD so I don't know what it was. Is there a way to format the SSD to Mac OS Journaled? I didn't see that choice when I used the Drive Utility.

The SSD is APFS. The hard drives are Mac Extended (Journaled). My 3 computers (MP 5,1, MBP 6,1 i5 and MBA 7,2 i5) are all 10.13.6. I did some additional checking this morning. After booting the MP in Target Mode using the MBP I observed that a drive with an old system build (10.12 I think) and the SSD both mounted on the MBP, however I was unable to open any files on the SSD with Pages, Numbers or Keynote. Also I was unable to move any files from or to the SSD. A TIFF file did open with Preview. I was able to open files on the old 1T hard drive as well as move files to and from the hard drive.

Incidentally, I have attempted to post replies two times only to return to the Forum and discover that they were not there. I hope this one gets through. Each time I clicked the Post button and see the post in the list. When I returned it was gone.