Booting from a USB drive on Windows 7 can be slightly confusing because there are two different methods depending on your situation:
During setup, if you see "Load Driver" or "No drives found" , it means your USB 3.0 drivers are missing or your SATA controller is not in IDE/compatibility mode. Change SATA mode in BIOS from RAID or AHCI to IDE (temporarily) or load drivers from another USB. how to boot from usb on windows 7
Most Windows 7 laptops and desktops have a "Boot Menu" key that lets you select a startup device without changing permanent settings. Booting from a USB drive on Windows 7