Follow Windows Reinstallation Guide/A Clean install of Windows 7 (or 8 using the 8.1 Consumer Preview .iso).
Note this is a Media Direct System and Media Direct partitions should be setup before the installation of Windows (Step 7b) for correct operating of the system. Sometimes pressing the MD button instead of the power button corrupts the entire hard drive if MD is not set up correctly.
Use the following drivers with Windows 7 XPS Laptops - Windows 7 (Unofficial Drivers).
Before installation ensure that you have carried out the extended preboot diagnostics by following the instructions on page 410 to make a diagnostics CD or USB and booting from it.
Note if concerned with the age of the hard drive you should consider installation of a SSD.