Why am I unable to install Windows 7 on brand new Mac Mini using a bootable USB stick?

[iMore Question]

the mini is new. bootcamp runs fine, creates the partition, but seems unable to boot from the usb. the usb stick has been reformatted several times at root level and is fat 32. i have tried using an iso image downloaded from microsoft, and one from a brand new licensed windows 7 disk (having created the iso on another machine, as the mini has no built in cd drive). after running bootcamp i just get a black screen. rebooting and holding down alt brings up o.s. disk, o.s. recovery and wininstall disk. (also small horizontal window called network with wifi logo next to it) . clicking on wininstall disk leads to black screen. clicking on network window leads to request for selection of wifi network and password. entering name of wifi network leads to endless spinning wheel; no chance to enter password. (all this although the mini is plugged into to ethernet). have taken machine to a genius bar who were unable to help other than saying the mini was "unusually formatted" and suggested i return it to apple. that has been done and i now have mac mini no 2. it behaves in exactly the same way. apple support took a log of the various key commands made during a support session and say there is nothing wrong with the mac or their software and it must be the stick or a microsoft issue. microsoft disagree. can anyone please give some clues or advice as to what to do next (i guess i can send it back again and get a pc, but i've been a macuser for 26 years and quite like them!)