How do I reinstall Windows and Office?

You need the product key for Microsoft Office in order to install it. If it came preinstalled with Microsoft Office you should have a MPI card:

http://dellwindowsreinstallationguide.com/download-microsoft-windows-and-office/download-microsoft-office/microsoft-product-identity-mpi-card/

As for Windows you can request a Reinstallation DVD or download a Retail Windows 7 Digital River .iso:

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

Install Windows 7 Professional without a product key and after installation use the Activation Backup and Recovery Program with Dell files to activate:

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

Note if you have lost your Microsoft Office MPI card, use the retail .iso to attempt to do a repair install and then use Belarc Advisor to recover the Office Product Key:

http://dellwindowsreinstallationguide.com/gathering-information-about-your-pc/belarc-advisor/

As Philip says, you can contact Dell support and request for a DVD.

Additionally, if your PC shipped with MS Office pre-installed (Starter Edition), you may not be able to restore it. Whereas, if you've paid for MS Office, you can claim the installation DVD for MS Office also.

Windows product key will be availble on the Certificate of Authenticity present at the back of the laptop, usually in the battery bay (remove the battery to see the product key).

Additionally, if your PC shipped with MS Office pre-installed (Starter Edition)

If looking for the Starter version note that it is obsolete and Office 2013 WebApps which are free to use have superior functionality:

http://office.microsoft.com/en-gb/office-online-help/get-started-at-office-com-HA101785172.aspx

They are however intimately linked to OneDrive and you should get 15 GB of free storage space.

Microsoft raised the capacity for OneDrive from 7 GB to 15 GB -- matching the rival Google Drive limits. Microsoft says that its research indicates that three out of four users have less than 15 GB of personal files on their PC, so it believes that the new 15 GB limit will accommodate the needs of the vast majority of users.

http://www.techrepublic.com/article/new-office-365-onedrive-storage-is-essentially-unlimited/