Q: Unable to boot windows bootcamp after updating to yosemite

Leave your Testdisk display and start a new Terminal Window. 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 Testdisk output (and you can verify) in Steps 7 and 8. Please notice the '+' sign in step 8. The text in parentheses is for informational purpose to describe the action being taken. Gdisk has one-character commands.

Rebuild GPT4 using start/end offsets

1. Sudo gdisk /dev/rdisk0
2. P  (print the full list of parts)
3. D  (delete)
4. 4  (part 4)
5. N  (new part)
6. 4  (part 4)
7. 490831872 - Start offset in bytes  (start point for Bootcamp part)
8. +485941241  - Size offset (as opposed to End offset)
9. 0700 (Windows part type)
10. P  (print list of all parts just to see what changes will be made)
11. W (Write the new GPT)
12. Y  (Yes! really write the new GPT)

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

Rebuild MBR to match the new GPT information thus resetting the Hybrid MBR. Use defaults for other questions (like partition codes). The only values that need modifications are the Boot flags and step 10. Accept all other defaults that Gdisk offers. Please see the sample Q&A as an example. These steps can be repeated if you make a mistake before you get to Step 12, otherwise start from Step 1 for these steps. Step 6 has numbers which are typed with a space between the numbers.

1. Sudo gdisk /dev/rdisk0
2. P  (Print list of parts)
3. R  (Recover)
4. O (print current Hybrid MBR)
5. H (chooses Hybrid)
6. Partitions numbers to be hybridized: 2 3 4
7. Y  (Good for GRUB question)
8. N  (part 2 boot flag)
9. N  (part 3 boot flag)
10. Y  (part 4 boot flag make NTFS bootable partition)
11. O  (print current Hybrid MBR)
12. W (Write the new MBR)
13. Y (Yes! write the new MBR)
14. Reboot

Here is sample Q&A for this section. Please notice the Press Enter/Return.

Place EFI GPT (0xEE) partition first in MBR (good for GRUB)? (Y/N): Y

 

Creating entry for GPT partition #2 (MBR partition #2)

Enter an MBR hex code (default AF): Press Enter/Return

Set the bootable flag? (Y/N): N

 

Creating entry for GPT partition #3 (MBR partition #3)

Enter an MBR hex code (default AB): Press Enter/Return

Set the bootable flag? (Y/N): N

 

Creating entry for GPT partition #4 (MBR partition #4)

Enter an MBR hex code (default 07): Press Enter/Return

Set the bootable flag? (Y/N): Y

Test 1 - Does Bootcamp Volume show up in Finder?

Test 2 - Can you see files in Bootcamp Volume?

Test 3 - Can you select Bootcamp in System Preferences -> Startup Disk?

Test 4 - If Test 3 is successful, select Bootcamp and Click Restart.

Yes. Are you executing the first set of Gdisk steps or the second set?

Type p then press Enter.

Type d then press Enter.

Type 4 then press Enter.

Type n then press Enter.

Type 4 then press Enter.

Type 490831872 then press Enter.

Type +485941241 then press Enter.

Type 0700 then press Enter.

Type p then press Enter.

Type w then press Enter.

Type y then press Enter.

You need to press Enter here. Please see the sample Q&A in my earlier post.

Very glad to see you are back in business. .

Please make sure you create fresh backups of OSX and Windows on separate external disks and use these as baseline for any future recovery.