unsupported configuration detected

This error tells you not to connect monitor to integrated video port while having a discrete video card installed.  Connect monitor to discrete card.

This is a bios message and cannot be bypassed.

You cannot use the Built onto the system VGA connector when there is a card in the X16 Video slot.

gx320 620 745 755 360 760 960 380 780 980 390 790 990

System halted!

Attention: Unsupported Video Configuration Detected

Action is Required

This computer has an add-in graphics card, but the monitor is plugged
into the integrated video connector.
To attach the monitor cable to the add-in graphics card:

1. Shut down the computer
2. Plug the monitor cable into the add-in graphics card connector.
This may require a video adapter or video adapter cable.
(provided with the system)
3. Turn on the computer.

This message should not appear after completing these steps.
For more information or help, please refer to the system documentation

The screenshot error seems to suggest you have connected a DP cable between integrated onboard DP port and a monitor.  you also said you connected an HDMI cable, which can only connect discrete video card and tv, as there is no on-board HDMI port.

are you sure there is nothing connected to onboard Display port?

that message only showed  when the graphic card was in  & hdmi cable hooked up to  tv

The message comes from the bios not windows.

This is always not supported.

The system will not boot hooked up that way.

when it happened i was on the card

made a mistake  it's  a 780dt NOT sff.

Somehow your 780dt detects a monitor connected to onboard DP port. Your card has only hdmi, vga, dvi.  Send a picture of your pc rear port when error occurs.

what card i had in.

post a picture of how you connect all the cables at rear side of 780dt when you have error shown on monitor.

with hdmi

great, motherboard

This is a bug encountered by multiple 780 users.  Looks like it is due to a bios glitch or defective motherboard.  

This happens with nothing displayport attached, nothing attached to the integrated ports.

try flash bios to latest version (understanding bios flash has risk to brick the board), if still no luck, and you can not use the integrated DP port for tv, consider replacing motherboard.

replacement board can be inexpensive $16.99 free shipping but seller may not be aware some boards are defective. better ask seller to test board using an add on low power video card and confirm no such error before purchase.