Hmm, you may have a bit of a problem on your hands being that you are dealing with an OEM computer, the Dell Studio XPS 8100 specs vary see
here if you contact Microsoft they very well may tell you to contact Dell and purchase Windows 7 recovery media and as the upgrade from 7 to 10 is no longer free you will have to purchase a separate product key for upgrading to Windows 10.
If you have access to a computer that has internet connection I would download a Windows 7 ISO from
here and give that a go, more computers shipped with Home Premium than Pro so would try Home Premium first, I prefer burning the ISOs to disk but in this instance USB thumb drive would be best as you may need to download a couple of ISOs if the original OS for the computer was Pro and not Home Premium, saves on a blank DVD if not right first time
Please note that after installing Windows 7 you need to upgrade to 10 so that the MB and Windows 7 details are stored on the Microsoft database, this will allow you to do a clean install of Windows 10 in the future without having to re enter your product key.