Going Around in Circles with Boot Camp Assistant

I'll try to be succinct: Using an iMac with Fusion drive. Using BC, partitioned it for Windows after downloading Windows updated software as per instructions to a USB drive. Computer restarted to a black screen that read in DOS: No bootable device -- insert boot disk and press any key. (BTW, the Windows disk is in a peripheral Apple DVD drive). Restarted holding the Option key, restarted BCA, selected third option on Task Menu (Remove Windows 7 or later version), hit continue and was given the option to restore disk to single partition.

Q: what happened to the partition I had already created for Windows?

Why do I need to start all over (as the step recommended will wipeout the OSX HDD)?

My Windows disk is a retail version that worked before, 64-bit Home Premium.

Hope I've included all the pertinent details. Oh, and am running Mavericks with all software up-to-date.

thank you in advance...