How to reinstall Windows 7 as an upgrade or a custom installation.

QUESTION Three years ago I bought an HP laptop running Vista with a free upgrade to Windows 7. The upgrade consisted of two discs: HP Upgrade Manager, which I had to run first, and a Windows 7 disc, marked 'For use only as an upgrade to a qualifying HP Windows 7 Upgrade PC'. The Windows disc has a valid Microsoft product key sticker. My overloaded laptop is now grindingly slow and it's time to reformat the hard drive and reinstall the OS.

Can I do this in the same way as the original upgrade, or will the fact Vista no longer exists on the computer cause problems? Anon

HELPROOM ANSWER Before starting this procedure, it's vital that you've backed up everything you need from your system. The Windows 7 upgrade disc should consider an existing installation of Windows 7 a valid operating system from which to 'upgrade'. Don't reformat your hard drive before you start. Instead, insert the Windows 7 upgrade disc and run the installation from Windows.

You can choose to complete either an upgrade or a custom installation. The upgrade option will perform what used to be known as a repair installation, leaving your programs and settings intact, but returning the operating system to its original state. You'll need to reinstall any Windows updates and drivers following the installation.

However, a custom installation won't clear out the bloat from the Registry. We'd advise opting for the custom installation. This will leave you with a fresh version of Windows, without your documents and applications, but with your previous installation backed up in a 'Windows.old' folder from which you can recover that data.

You may run into trouble if you wipe your hard drive before you begin the procedure. The upgrade key is unlikely to activate your installation if a valid upgrade hasn't taken place. There are workarounds for this, such as installing Windows 7 twice or employing a Registry hack to fool the system into thinking it's a valid upgrade. However, we recommend avoiding this; while no problems have been reported so far, it's feasible that Microsoft might flag up such activations as invalid in the future.

The HP Upgrade Manager disc contains versions of HP's preinstalled software that were previously compatible only with Vista. It's designed to manage the upgrade process for you. It may be wise to start by running this disc first as HP may have customised the installation discs, making them slightly different in operation from the standard Windows installation media.