I have a Dell Optiplex 780 SFF (From what I read it has UEFI) with an internal hard drive I cannot boot from and I'm wondering If I can use my Seagate Expansion Desk 1TB like if how you would use a USB flash drive/stick to install windows from? if so do I have to format and clean the disk using diskpartition and remove all data? can I keep some of the files and just boot from a new partition I make? Because I have about 500 gb occupied and I made a new partition called X: New Drive and used bootrec command on it and placed the windows installation files on it. but my Dell won't boot from it even though it recognises the device as "USB Device" I also changed the boot order to set priority to USB Device and tried setting Sata handling from RAID to Legacy but no luck there. I'm kind of losing hope and thinking If I should get a flash drive but if possible I'd like to use this external drive to install windows from OR if possible install a bootable windows OS into this drive. there are files on this external drive AND the internal drive of the Dell so If possible I would want to access them.. I have a NEC laptop I'm doing all this work on from that is running Windows 10 if that matters. any help would be appreciated!