My guess it would be an external dvd drive or service equipment for computers without any internal boot  capability. The 5060 model is not a regular computer. It looks like the devices in doctor offices that are mounted on various stands or stations without any device slots or controls. See pictures--

http://www.dell.com/en-us/work/shop/desktop-and-all-in-one-pcs/optiplex-5060-micro/spd/optiplex-5060-micro 

edit: These are "thin clients" for business--- http://www.dell.com/en-us/work/shop/wyse-endpoints-and-software/wyse-5060-thin-client-cto/spd/wyse-d-class/xcto5060thinclient

High-performance thin clients with quad core processors, designed for secure and easy-to-manage virtual desktop environments.

Sorted my own problem in the end, as you do.

Rebuilt my USB boot drive using Rufus (https://rufus.akeo.ie/) but using the UEFI compatible format.  When I booted with the BIOS in default mode (UEFI, Secure mode) it appeared as a bootable device and ran fine from there.

So what has changed is that the BIOS will no longer install an OS to an internal drive using the previous boot disk format (I've been using this for years https://www.microsoft.com/en-us/download/windows-usb-dvd-download-tool). And interesting that neither the Dell support desk, nor the engineer who turned up on site knew this.  And even the OS install disk he had been supplied with for this incident was formatted in the old way so wouldn't work.

Every day's a school day.

Pretty standard bit of kit - http://www.dell.com/si/business/p/optiplex-5060-desktop/pd.

You cant boot windows 10 via USB unless its USB3 and Native to windows and is using Windows to GO for the Enterprise version of windows.

https://www.youtube.com/watch?v=vp9shHW57pk

If you have all the pieces including the correct version of RUFUS it works fine.

There is no windows 2 Go for windows 7 or earlier.

Did you ever get the Windows 10 image to stay on the HD? I haven't been able to do so. I can install Windows 10 on the computer with the USB, which it is booting from the USB. When I take away the USB then there is no bootable device. In the BIOS it does recognize that the system has a 500 GB HD but when you boot into F12 the HD is not recognized. SO I called Dell and they sent a rep out to change the motherboard on the two systems we have. The new motherboard was not the problem since it did the same exact thing. The Dell rep had no clue to why it was doing that and urged me to call the Core Support for Dell, which I did. After two hours talking with many departments I finally found the person that sent me two new systems. I received those two system last week and I tried to image windows 10 E and it did the same exact thing that I originally had the issue with. 

If anyone has encountered this problem please get back to me with a solution. Any and all help would be greatly appreciated. 

Jerry J. Perez

IT Tech I

Texas Tech University

You cannot boot the os to USB drive without Windows 10 enterprise and Windows 2 Go install.

F12 Booting is not recognized without Secure Boot OFF and CSM with Legacy option roms on.

CLASS 3 BIOS HAS NO CSM.

https://www.youtube.com/watch?v=VpZJpzPvqtk

We are having the exact same problem. Dell Opti 5060. We are trying to put our own image on using USB. Boot with F12 and it doesn't see the flash drive listed under UEFI. We switch it to Legacy Mode and It sees the flash drive there. It acts like you installed WIndows. Pulled flash drive out and rebooted, but it says there is no boot device. 

We can't even update the BIOS through the USB as it doesn't see that path.

We have tried every combo we can think of, but not able to install our image via USB. 

We are using Win 10 Education btw

Newer systems (industry wide) no longer support booting in Legacy Mode, except to external devices. This is because Intel is planning on removing all legacy BIOS support by 2020. Going forward, any image to be installed on an internal drive will need to be UEFI:

https://www.dell.com/support/article/us/en/04/sln309720/newer-dell-systems-unable-to-boot-to-internal-boot-device-in-legacy-boot-mode?lang=en

---

@DELL-Alasdair R wrote:

 

Newer systems (industry wide) no longer support booting in Legacy Mode, except to external devices. This is because Intel is planning on removing all legacy BIOS support by 2020. Going forward, any image to be installed on an internal drive will need to be UEFI:

https://www.dell.com/support/article/us/en/04/sln309720/newer-dell-systems-unable-to-boot-to-internal-boot-device-in-legacy-boot-mode?lang=en

 

 

---

There is a critical element you did not indicate that will confuse people.  Windows 2 GO installs are USB only.

Taking an installed internal drive out and putting into an enclosure WILL NOT BOOT OR WORK.   You would have to reinstall from scratch in "Windows 2 Go" mode.

This is what was done in the post above on a steam machine.