Please note: during this procedure you’ll lose any data on your USB flash drive. Please be extra careful during formatting, choosing the wrong drive will erase it completely. This guide provided as-is, at your own risk.
You will need:

PC running Windows XP/Vista/7/8
Windows 7, 32/64-bit (depending on the system) installation disk
USB drive with at least 8GB of free storage

Preparing the USB drive:

Open command prompt as administrator – Right click on Start > All Programs > Accessories > Command Prompt and select Run as administrator or type cmd in the Start search bar.
Run diskpart utility by typing diskpart into command prompt window and pressing “Enter”.
Locate your USB drive disk number by executinglist disk. We’ll assume the USB drive is 1.
Run the following commands:
select disk 1
clean
create partition primary
select partition 1
active
format fs=NTFS
assign
exit

Now we have prepared USB drive. Lets make it bootable:

Insert Windows 7, 32/64-bit installation disk into DVD drive. Let’s assume it’s D
Go to D:\boot (cd d:\boot)
If your USB drive letter is “e” please run bootsect /nt60 e:
Copy DVD Windows 7 media content to USB root folder (etc. don’t put it into any folder)

You are now ready to install Windows 7 from USB flash drive.

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