"Non bootable disk" error after Boot Camp installation

I have Yosemite 10.10.3 on a 2010 Mac mini Server. Although it doesn't have an optical drive, this specific model doesn't natively support installing Windows from an imaged USB thumb drive, for some reason.

Thankfully there are lots of tutorials online on how to remove a single string in the plist file in the Boot Camp Assistant application package contents and re-signing the application. After doing this, BCA gives me the option to create a bootable USB installer from an ISO, which I did. I had BCA download the latest drivers, partition my Mac's second internal HDD for Boot Camp, and download support software as well as install Windows 7 following an automatic restart.

Well, the Mac restarted but a Windows DOS screen immediately loads and says "Non-system disk. Press any key to reboot." If I boot up holding down the Option key, the bootable USB Windows installer created by BCA doesn't actually show up.

I don't have an external optical drive and I've tried everything I can think of. Two different brands of flash drives, the USB port closest to the power cable, using Boot Camp Assistant to create the bootable installer, et cetera.

It may be that since my Mac doesn't natively support installing Windows from USB that BCA didn't do the final step in making the USB drive bootable. Is there a way to manually do this from a Mac or PC on the thumb drive thy already contains the Windows installer as imaged from the ISO?

I'd love to get a Windows 7 up and running on my Mac. Thanks for any help!

satcomer said:

Did you do a noob mistake and FORMAT the whole drive when formatting for NTFS Windows 7?

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I had Boot Camp Assistant (successfully) partition my Mac's second HDD leaving 30GB for Windows. It completed without error and there was never an option to choose formatting since BCA presumably uses the needed settings for a Windows 7 partition.

Similarly, it also obviously formatted the USB thumb drive when imaging it with the Windows 7 installer ISO in the appropriate format. I had formatted it as FAT beforehand.

satcomer said:

Then if you installed the drivers for the Windows partition then their should be a Boot Camp Control panel installed to choose the OS X partition, if it is still there.

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To choose the OS X partition from where? BCA? After creating the USB installer and partitioning my HDD, BCA restarts and is supposed to boot into the installer, but like I said I unfortunately get the "Non-bootable disk" error. Any ideas on what's causing that? I think I've done everything right up until the error.

satcomer said:

Boot into Recovery Mode and use Disk Utility on your internal drive and choose your startup disk.

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I can start my Mac and boot into Yosemite just fine though. It's after BCA created the USB installer, partitioned my drive, and restarted for the Windows installation that my Mac gave me that DOS message.

Since then, I can restart into OS X normally. BCA couldn't rejoin the partitions (AKA delete the Boot Camp partition) but restarting in Recovery Mode and using Disk Utility unified the partitions in less than a minute. I tried to re-do all the steps after restarting into OS X, but BCA said it couldn't partition the HDD (even though it had just done this before) to create a Boot Camp volume. I'm backing up the HDD, reformatting it, and planning on retrying again.

satcomer said:

When I installed Windows 7 Professional I had to fomat the extra hard drive in my 2008 Mac Pro NTFS before it would install. The Boot Camp Windows drivers installed great after that install.

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At what stage? In OS X using Disk Utility? Or from the Windows installer after rebooting?

I did a lot of research and hit a new roadblock; Windows 7 won't install since I'm trying to install on my Mac's second internal HDD. The Windows installer gets confused if you have multiple internal HDDs and try to install Windows on any disk/partition that isn't the first HDD, or "disk 0."