Just thought I'd add, I've installed win 7 and 8 numerous times on my Mac mini and always get the exact same issue mentioned above.
However, the fix for me is very easy, format the drive again in windows setup, then just reboot, hold alt to get the drive selection, select your windows usb/cd drive and go through the process again and it will work.
Works for me every time, no need to do anything else.
I just successfully installed Windows 8.1 Update 1 on BootCamp on Mac OS X Yosemite. Here is a step by step I just wrote, hope it helps y'all:
How to successfully install Windows 8, or above, on Mac OS X Mavericks or above:
1- Windows OS ISO Image file
2- An 8GBs USB Flash Drive
3- A good Internet connection as you will need to download the Windows compatible drivers for your Mac
1- Open up Disk Utility and create an additional partition for Windows formatted as ExFat. 100GBs, or above, is recommended as update to the operating system, as well as Apps requiere space on your HD or SSD [This step can be done during Mac OS X's installation process]
2- Open up BootCamp Assistant
3- Make sure only the 'Create a Windows 7 or later version install disk' is checked and your USB Flash Drive plugged in and click 'Continue'
4- Click 'Choose' and select your Windows ISO Image file
5- Select the USB Flash Drive you will be using during the installation process and click continue to confirm
6- Once done, restart your Mac and hold down the 'alt/option' key on your keyboard to bring up the Boot Menu
7- Select the USB Flash Drive named Windows, not the UEFI Boot
8- Install Windows as you normally would
* Remember to press and hold the 'alt/option' key, and select the Windows Partition, whenever the installation process requires your Mac to restart