This is the most common error when installing Windows 7 on new hardware. It happens because Windows 7 setup doesn't know how to talk to the USB port.
You can also use the Windows 7 USB/DVD Download Tool to automate this process. Phase 2: Enter BIOS/UEFI Settings how to boot from usb windows 7
Most modern and late-era Windows 7 PCs have a "One-Time Boot Menu" that lets you select the USB without changing permanent settings. This is the most common error when installing