Hi ChrBau13,

Welcome to the Dell Community,

Thank you for posting on Dell Community Forum, since the system was shipped with Windows Vista and later you upgraded the same with Windows 7 you’ll first have to do a clean installation of Windows Vista. In the process of installation you’ll have to select OS drive, format it and continue with Vista installation. Once the installation is completed you can upgrade the same to Windows 7.

Note: Please back up all your data (personal files, folders etc) before proceeding with OS installation.

Please follow the below mentioned link and use the steps on How To Restore or Reinstall Microsoft Windows on a Dell Computer.

http://support.dell.com/support/topics/global.aspx/support/kcs/document?c=us&cs=19&l=en&s=dhs&docid=DSN_362048&isLegacy=true

Please reply to the post if you have any further queries.

Thanks & Regards

Dell_Aryan_V

Dell Social Media Responder

It depends, have you replaced the hard drive?

If you have the same hard drive and are just reinstalling it. You should be able to boot from the upgrade DVD directly via BIOs. Follow my wiki A Clean Install of Windows 7 for best results. Note the part which mentions DBAN will wipe the drive completely but if you do this then the upgrade DVD will detect no earlier OS and so you may run into issues so I recommend skipping this step in your case.