Macbook Air Bootcamp issues

I went through the wizard on my 2012 macbook air and created a bootable (or so i thought) USB for Windows 7. I've been through the USB process twice now to make sure that wasn't the issue.

Anyway, i clicked install windows, and then i heard the startup chime then grey for a big then the screen just went black and nothing happened. I assume it turned off.

I tried again and hit option at startup which showed me the USB and my OSX HDD. When I clicked the windows USB option i got the same thing as about. Grey screen then black/off.

The only way to boot back into OXS was to hold option and manually select it.

Any ideas?

 

Will try another USB. The Iso is fine as I used it to set up a vm a few days ago. Other suggestions ?