Q: Lost boot ability to OSX and Windows 10

Please post the output of the following Terminal commands.

diskutil list

diskutil cs list

sudo gpt -vv -r show /dev/disk0

sudo fdisk /dev/disk0

The "sudo" commands will prompt for your password, and it will not be echoed back. You may also see a warning about improper use of "sudo" and potential data loss due to "abuse" of the command.

Boot into Internet Recovery (OS X: About OS X Recovery - Apple Support) and OS X: Installing OS X on an external volume - Apple Support and boot from the external disk. If you have a second Mac, you can also Share files between two computers with target disk mode - Apple Support .

Install GPT Fdisk (http://sourceforge.net/projects/gptfdisk/) on the Windows side and run gdisk32.exe from an elevated CMD prompt window. When prompted, use '0:' as the disk (zero-colon without the quotes) and post the output of 'p' command.

1. You do not have a GPT 2 entry which is typically OS X. GPT2 should start at 409640 and end at 195715463.

2. Do not modify the GPT or MBR, it will lead to catastrophic failures.

3. Type 'r' (recovery).

4. Type 'o' (show hybrid MBR)

5. Post the output.

Using both the GPT and Hybrid MBR to reconstruct the full GPT gives us the following disk layout. Please verify the numbers before we start the fix.

EFI - 200MB, OSX - 93GB, Recovery HD - 605MB, Shared - 92GB, Bootcamp - 279Gb.

We are going to

1. recreate the missing GPT 2 entry.

2. delete GPT 4.

3. create a new GPT 4 (Shared?). This is not your Bootcamp as you can tell by the start/end disk addresses.

4. create a new GPT 5 (BOOTCAMP). This is the bootable entry in your MBR as shown by the start/end disk addresses.

Your MBR will be untouched leaving Windows bootable.

You need to use the following steps. If you see any error messages during the following steps, please stop and post back here with the error message. The following steps have values from your GPT and MBR output (please verify for any typing errors). The text in parentheses is for informational purpose to describe theaction being taken. Gdisk has one-character commands except when entering numbers.

Rebuild GPT entries using start/end disk addresses

1. P  (print the full list of parts)
2. N  (new part)
3. 2  (part 2 - OS X)
4. 409640 ( - Start offset in sectors or the start point for OSX part)
5. 195715463 ( - End offset)
6. AF00 (HFS+ part type)
7. D (delete)
8. 4 (part 4 - old Bootcamp)
9. N (new part)
10. 4 ( Shared part)
11. 196986880 ( - Start offset in sectors or the start point for Shared part)
12. 390836223 ( - End offset)
13. 0700 (Microsoft Basic Data)
14. N (new part)
15. 5 ( Bootcamp part)
16. 390836224 ( - Start offset in sectors or the start point for Bootcamp part)
17. 976773119 ( - End offset)
18. 0700 (Microsoft Basic Data)
19. P  (print list of all parts just to see what changes will be made)
20. W (Write the new GPT)
21. Y  (Yes! really write the new GPT)

This will delete and re-write the GPT partition info for /dev/disk0s2, /dev/disk0s4 and /dev/disk0s5.

You should now be able to see OSX and boot into it. Once you are able to verify OSX we can do the next step.

You can ignore the default value that Gdisk shows. Use AF00, since this a new GPT 2 and is pointing to HFS+.