This is Alienware focused, but the Recovery procedures and/or clean-install are the same.

Also contains link to request a new Dell-OEM Windows-7 disk (as long as computer shipped with that OS).

Install key should be on sticker attached to PC.

http://en.community.dell.com/owners-club/alienware/f/3746/t/19376654.aspx

That method is far too technical. All I want to do is use Windows to format the hard drive and re-install my copy of Windows 7.

I have found a Windows 7 Home Premium 64 bit physical disk and don't know if it's for the copy of Windows on this system or not. I have the Product Key written on the sleeve but how do I find the key on this computer to compare it?

Is the disc a Dell Windows 7 Reinstallation DVD or a Retail Windows 7 Installation DVD?

A Dell machine with Windows 7 will have a COA affixed to it unless it came with Windows 8.1 Professional with downgrade rights to Windows 7 see here for details:

http://dellwindowsreinstallationguide.com/a-clean-install-of-windows/the-oem-or-retail-license/

Note if it is Windows 7 Professional that is preinstalled the Windows 7 Home Premium installation DVD will not do for installation.

You can call Dell Technical Support to procure a Windows 7 Reinstallation DVD. The Dell Windows 7 Reinstallation DVD will use System Locked Preinstallation which ill input a generic product key automatically and automatically activate when a valid Dell BIOS is detected.

Alternatively you can backup this product activation using the ABR program:

http://dellwindowsreinstallationguide.com/a-clean-install-of-windows/microsoft-product-activation/the-activation-backup-and-recovery-program-windows-vista-7-version/

You can download a Windows 7 .iso from here and create a bootable USB:

http://dellwindowsreinstallationguide.com/download-microsoft-windows-and-office/download-microsoft-windows/windows-7-sp1-iso-download/

Once you have installed Windows 7 you can restore the product activation using the ABR program. See A Clean Install of Windows for detailed installation instructions:

http://dellwindowsreinstallationguide.com/download-microsoft-windows-and-office/download-microsoft-windows/windows-7-sp1-iso-download/

 

Try this page, it's less technical.

<ADMIN NOTE: Broken link has been removed from this post by Dell>

But based on your comment, to see this project through to successful completion ... you might have to seek professional assistance.

The first part of the techical page explains how to do a Dell Restore, which is simpler.