Try using a USB stick instead, it will probably work better, I think maybe a 8 GB or 16 GB one or more should do the trick. Slightly costlier than the blank DVD however.  Alternatively you may ignore the Dell DataSafe program and follow the in depth guide I wrote (link below) which tells you how to obtain/download and make a Windows 7 installation disc/bootable USB stick from digital river. Then it goes into further detail about the installation procedure, the Dell System Drivers and the preinstalled software. The guide I wrote focused on English .iso files and English Updates but the Spanish ones are here. You will need to find the Spanish Service Pack 1 (actually the same link I provided for the service pack 1 just change the language from English to Spanish). You need to find the Spanish Internet Explorer 9 yourself though because I can't read Spanish. You may use this .iso file alongside you're Dell Product Key however it will require phone activation. I would download the .iso file and keep it handy on an external hard drive just in case. Once you have the file you can always make a bootable DVD or bootable USB stick. The guide tells you how to do this from the .iso file and where to get everything else you need. I have made a request in Dell Idea Storm that Dell make available to download Windows .iso files for this type of situation. (For example when Windows 8 comes out, Digital River will stop selling Windows 7 and these download links will become unavailable as have the Vista download links they used to host). In this case you would be able to download the .iso file direct from Dell and use it to install Windows 7. Phone activation would not be required in this case. Please promote the idea on idea storm (link below) and maybe they will see about implementing it.
Hi there! I am from Spain and I recently purchased a Dell XPS L702X and no OS media, as I wanted to create the recovery disks as soon as the laptop arrived. When I was doing the backup through Dell Datasafe, the program always stop verifying the first DVD-R, it never carries on to record the second DVD-R(obviously I tested the DVDWriter burning other stuff and it works flawlessly). I contacted DELL and their answer is that I should have ordered the DVDs, that Datasafe is a free program and they can not guarantee it works! Unbelievable! I paid a licence of Windows 7 with the laptop, and if they don't send the medida, at least they have to provide the necessary tools to record the recovery media yourself, but not wash their hands if the toos does not work!This is my second Dell Laptop, and it will be the last one. Their customer service is not as good as it used to be. 
Dell is unbelievable!