Why does my Windows 7 ISO file not boot when written to a USB stick?

I need to write a windows7 iso file on my usb stick. I had been used to this task. I usually either use the dd tool, or unetbootin. Surprisingly both don't work today. With dd I did the following : dd bs=4m if='windows7.iso' of=/dev/sdb My new supposedly bootable usb stick wont boot. Ok so I used unetbootin. This time, I get the unetbootin bootloader screen, but windows7 is not listed. Only the default choice is left. In either way, I failed at creating my bootable stick. Few months ago, I could make this same USB stick boot with the very same ISO file. I also did the same tasks after formatting my stick withh this command: mkfs.vfat -F 32 -I /dev/sdb There were no difference as expected. I am probably doing something wrong here, but I can't see where my mistake is. Any idea on what is going on?