You will have to make the USB drive bootable. Google how to install Win 7 from USB drive and you will find all the info. Of course you will need access to a working PC to set up the USB drive. I assume you have an ISO file on the flash drive. You will have to save it somewhere else since you will lose everything on the flash drive when you make it bootable. Then follow the directions you find on Google.
One nice advantage of this is it is a much faster install than a DVD.