How to Install Windows 7 from USB (Flash) Drive
Step 1: Create a bootable USB drive
1. Start UltraISO (V9.3 or newer version, download here)
2. Choose ‘File’->’Open’ from main menu and open ISO file of Windows 7, for example “d:\ISO\WIN7_DVD.iso”; You may also open the original DVD by 'File'->'Open CD/DVD' from main menu if you have not an bootable ISO
3. Choose ‘Bootable’->’Write disk image’ from main menu
4.Insert the USB drive you intend to boot from
5. Choose proper “Write Method”,USB-HDD+ is recommanded
6. Hit “Write” to get a bootable USB drive
Step 2:Configure the BIOS of your computer
You should now reboot and go into the BIOS configuration to boot from USB. Instructions for doing so wildly from system to system, but generally entail the following:
1. Reboot the system.
2. While booting (before Windows starts loading), get into the BIOS configuration screen by hitting something like F1, F2, Delete or Escape. Hotkey instructions are generally provided on the screen.
3. Go to the section that contains your boot devices.
4. With your USB drive plugged in, the USB drive should be listed. If it isn’t, your system might not support booting from USB. Assuming that it is supported (as is the case with virtually all modern hardware), promote your USB drive to the primary boot device.
5. Exit from the BIOS configuration, saving all changes.
If you’re completely new to BIOS configuration, BIOS for Beginners over at Tom’s Hardware might be a good primer. Be aware though, that you can seriously screw up your system by providing incorrect settings!
Step 3:Boot and setup Windows 7 from USB
Assuming that you properly configured your BIOS and your USB device supports booting, Windows 7 setup program should now load, you can now continue to finish setting up Windows 7 from USB drive. Depending on the speed of your USB device, this may take a while.