Windows 8.1 installer can not find any disk partitions at all in boot camp 5.1

Hello

I have purchased a new Imac 27" latest model with Mavericks pre-installed. I am trying to install windows 8.1 pro with original disc 64 bit in Boot camp assistant 5.1. I am using a usb dvd writer to read windows disc. I have rebooted into the windows installer after mac finised downloading the windows support software into my 64 gigabyte flash drive which is formatted in ms dos fat 32 format. I made it too "Where do you want to install windows" screen but problem is there are no drives showing at all to select. The space where you usually see four partition drives with the bottom one named Boot camp, that space is totally empty showing that there is no internal hard drive at all....simply shows a error at the bottom can not find any drive. Please Help!!!!!!

The mac os is running fine if i restart the mac and cancel windows installation. I have gone into boot cam assistant to delete the windows partition and retry but the same problem prisists. Plz help.