That is a 16 year old computer and it stopped getting bios updates long ago. It does not have drivers for windows 10 or Windows 7 or 8. There is no bios update.  Support for Dimension E521 | Drivers & Downloads | Dell US
Greeting:  Re : Dimensions E521  Win 10 Pro   I went in to Dell downloads to download the latest version of the BIOS which I believe is 1.1.11 2007 and was met with a pop up saying to make sure I am signed in as the Administrator.  Having done that, I tried again and got the same pop up. Am I missing something?  
Having to do with Administrator