Mac – Why didn’t the Windows partition show up in the Startup Disk preference pane

I had a similar issue and the below trick solved it.

Resetting NVRAM

1. Shut down your Mac.
2. Locate the following keys on the keyboard: Command (⌘), Option, P, and R.
3. Turn on your Mac.
4. Press and hold the Command-Option-P-R keys immediately after you hear the startup sound.
5. Hold these keys until the computer restarts and you hear the startup sound for a second time.
6. Release the keys.

^{Source: https://support.apple.com/kb/ht204063}

I need some more information before I can answer your question. First, what model is your mac?

Second, please run the following commands from the OS X Terminal app. Please post the results for me to read.

sudo diskutil list
sudo disktuil cs list
sudo gpt -r -vvv show -l /dev/disk0
sudo fdisk /dev/disk0

All these commands do is list information about your disk. They do not change anything. The commands may ask for your login password. This is normal.

I am trying to determine if you are using coreStorage. If not, then the problem might be the age of you computer. The drivers for windows 7 may not be compatible with OS X 10.10.

See this Apple Support Communities post: windows 8 does not recognise Macintosh HD, No drive Letter.

Just a note about the article you reference:

The article is full of problems and errors. While it is true the default partition names are "Macintosh HD" and "BOOTCAMP", often users change these volume names. The author should have known this. Also, if you follow the instructions in the section titled "Create a Shared FAT32 Partition", your computer will not be able to boot to windows. The reason for this is simple: Windows can only see the first 4 partitions on your disk. The first partition is the EFI partition. It is normally hidden when viewed in the Disk Utility. The second partition is the HFS+ OS X boot partition. The third is the recovery partition which is hidden also. The Fourth is used as the Windows Bootcamp partition. If you try to insert a FAT32 partition, the Bootcamp partition would become the fifth partitioned, thus preventing windows from booting.

Update:

Well, you are using Core Storage which is probably the problem. Windows does not recognize partitions using Core Storage. My understanding is that Yosemite converted your OS X partition from HFS+ to Core Storage. You need to change it back to HFS+. klanomath at Can't make more than two partitions seems to have the answer. Here he has solved a different problem, but his solution steps should work for your problem as well. I would follow his steps with some minor changes. I have listed them below.

For his step 1, I would just use the recovery partition already on your disk. In other words, press the alt key while booting and select the recovery partition to boot to.

For his step 3, the command would be:

diskutil cs revert 4BB22737-5EFB-49D6-ADF1-5B719538AF45

Omit step 5.

Also, I would use the Disk Utility to backup the partition before entering the above command. This would require an external disk to store the image on, which you may not have. If you wish to do this and do not know how, let me know.

Let me know how things turn out and don't forget to give klanomath some reps.

dave