Bought Alienware X51 from Dell Outlet UK store, require Windows 7 reinstallation DVD

You should call Dell Technical Support UK and request a Reinstallation DVD.

http://www.dell.com/support/incidents/uk/en/19/Phone/HomeContact/s/n

If you have difficulties with that you can use the ABR Program and a Windows 7 .iso.

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

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

I advise carrying out the ABR backup as its an Alienware. The cert files should be the same as Dell however.

Follow my Windows Reinstallation Guide to Clean Install:

http://dellwindowsreinstallationguide.com/a-clean-install-of-windows/

Because it can be used to backup and restore the SLP activation mechanism of factory settings and the Dell/Alienware Reinstallation DVD. If you use the Digital River .iso (Retail .iso), you can install without a product key (skip product key) and then use the ABR program to restore the factory settings Dell SLP activation.

The other activation mechanism requires inputting the product key on your Windows COA see here:

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

Then phoning Microsoft for phone activation:

http://dellwindowsreinstallationguide.com/a-clean-install-of-windows/microsoft-product-activation/phone-activation-windows-vista-7/

Unfortunately the key on the COAs is prone to fading (Dell tend to shield them in battery compartments).

I recommend using the ABR program as its much more convenient than phoning Microsoft.