How to install Windows 7 or Windows 8 from USB – clean install, no disc needed

This guide allows you to perform a completely fresh install of Windows 7 or Windows 8 on your PC. This guide:

• Uses no discs. All the required files are downloaded from the internet and saved to a USB stick.
• Can be used for a computer with a new or blank hard disk
• Can be used to start again and wipe over a previous Windows installation
• Is fully legal!

tl;dr version

• Download Windows 7 ISO from Digital River
• Copy ISO to USB stick using Windows 7 USB DVD Download Tool
• Install Windows 7 with USB stick. Use key if finishing with Windows 7, otherwise no need to add a key
• Once installed, immediately download the Windows 8 Upgrade Assistant. Install Windows 8 from here.

What you need

• The computer you want to install Windows on. Its hard drive should be at least 60GB for Windows 7 or around 120GB for Windows 8 (Win8 on 60GB only leaves around 22GB once installed!). Check whether it’s 32 bit or 64 bit.
• Blank USB stick, at least 4GB
• Another portable hard disk (if you need to back up data)
• Another computer, already working, with a decent internet connection
• Licence key for Windows. Bear in mind whether you have a key for Windows 7 or Windows 8. This isn’t a guide on how to use Windows without a key!

A note about licence keys

A licence key is needed to validate that you have a legal and licensed version of Windows. Strictly speaking, this usually means one licence number per computer, and Microsoft maintain a record of which licence key is associated with which computer. When you ‘activate’ a new licence, you are telling Microsoft to tie your licence number with the computer you are activating it upon. Usually this is a one-way process (especially for OEM, student and other such discounted licences), meaning you cannot transfer the licence to another computer. This is also why an internet connection is required to activate Windows.
In reality however, the licence number seems to be tied specifically with the computer’s motherboard. You are free to reinstall Windows and activate your key on a computer as many times as you like, as long as the key was always vaid with that particular machine. Of course, if you try and install Windows using somebody else’s key, the activation is going to fail because Microsoft’s records will indicate that particular key has already been activated on a different computer.

Before you start…

If the computer already has a copy of Windows on it, then back everything up! Copy everything you might want to keep onto the portable hard drive such as music, photos and videos.
If the hard drive is new or blank, then it may need formatting.