RE: "A required drive partition is missing"
You can Download a Windows 10 TH2 .iso and clean install with your Windows 8.1 OEM Product Key. Follow the instructions here to clean install Windows 10 and then install the system drivers:
I made these using my Inspiron 13 7347 so it should be almost identical in your case.
Tech Enthusiast and Author of the Unofficial Dell Windows Reinstallation Guide