I bought an XPS 15 (L501X model) new several years ago. It came with Windows 7, which I still have installed. It did not come with any recovery media or Windows CD, but did have a recovery partition.
At some point when Dell backup and recovery was downloading an update for the recovery partition, it crashed, and the partition was left in a half updated state. I can't recover via the partition any more as it seems to be corrupted by the partial update process.
I am giving this laptop away and want to restore to factory condition. Certainly without paying for a Windows license since I have a valid one already that came with the notebook.
I have found this document helpful when restoring Windows. Along with basic instructions on how to restore Windows you will find means for requesting backup media. If you are in the US, Canada and the UK you can use this form to request backup disks, just scroll down about half the page and key in your service tag and click continue.
I will be sending you a friend request to get your information if you require further aid.