how to set my dell inspiron 8500 to factory settings
You mean the BIOS of your system or your OS or Windows operating system?
if it BIOS then make it as default by going to BIOS and If you mean operating system. Then You can use recovery cds which comes with dell or check if there is recovery partition. you can boot from there and install the new system.
You will need a windows CD, either one that came with it, or one that is retail.
If you can get the one that came with it, it will have all the fkn drivers an shit that the computer needs already on the CD, if you get a retail copy of Windows, then you will have to download the drivers for some things very likely once you get windows installed...
Insert your Windows CD, press any key to boot from CD when it asks
go through the setup, and when it gets to the hard drive selection, select your drive and delete the partition, then install on the blank space using NTFS (quick format)
Continue through the setup until windows is installed. Then go to Dell and download any drivers you may need.