Windows 7 Installation problem

I am trying to install windows 7 on my late 2012 IMac with an 32 gig flash drive. after bootcamp puts the files on the usb(including windows support software) my mac reboots and the windows 7 wizzard starts. after I click install now, a windows shows up asking me to select the drivers to be installed. I click browse and select the drivers folder, it tells me that no drivers have been found. i've read that this step should appear after i install windows 7. what's the problem?