Q: An error occurred while partitioning the disk

1. Try safe mode if your Mac doesn't finish starting up - Apple Support and boot back normally and test BC Assistant again.

2. Resolve startup issues and perform disk maintenance with Disk Utility and fsck - Apple Support and boot normally and test BCA again.

3. Try the following two steps and then try BCA.

     Resetting the System Management Controller (SMC) on your Mac - Apple Support

     How to Reset NVRAM on your Mac - Apple Support

4. If none of the above work then

     a. Back up OSX using Time Machine - Mac Basics: Time Machine backs up your Mac - Apple Support.

     b. Boot into Internet Recovery - OS X: About OS X Recovery - Apple Support.

     c. Erase your internal drive and restore from the TM backup in Step 4a - OS X Yosemite: Recover your entire system.

     Please be aware that TM does not backup Bootcamp partitions.

Please try the steps noted in that order.

What is the year/model of your Mac?

What is the year/model of your Mac?

There are several reasons for a black screen/no bootable device. The answer to the above question will determine the resolution. If you modified Bootcamp info.plist to create the USB, the USB installer will not work.

Excellent. Please ensure you create backups for OS X and Windows to separate external disks.