I take it that if you press F2 for BIOS, you're unable to access?

Take the battery out and power on.  It should say "System voltage is low," then give the option to enter into BIOS.  With the battery back in, try again.  Please let us know the results.

It's smart of you to post the error code.  Unfortunately, the description for that diagnostic Dell gives for that is vague.  Dell Diagnostic Indicators 

>stuck on this screen. bar not load and see color logo screen not normal.
>I can not press F2 F12 or any key. Unable to access bios.
>And then Black Screen & Blinking Cursor.
>Diagnostics LEDs 1-2-3, Power LEDs Solid green.

I think Bios damage while change the new bios battery.
Press F2 stuck on this screen. Bar bios not load.
I must change motherborad or bios ship?...
Thank to help me.

Changing the battery shouldn't have negatively affected BIOS.  But I think your right - BIOS is damaged or corrupted.  It's like it was just waiting for an excuse to go out.  Unfortunately, the 780 isn't a model with BIOS recovery.  Options basically are different MB or newer PC.

You likely won't be able to to get a new MB, but there's plenty of refurb and used MB's on ebay.  Be sure to get at least a 30-day return policy just in case if you go that route.

Others may chime in as well, but I really don't think your MB is recoverable if you can't even enter BIOS.  I see you can't even use F12 to access Boot Menu.

When you changed the battery, did anything accidentally short out that you know of, or anything get accidentally dropped on the MB?

Thank so much.
I make it very soft not accidentally dropped. My MB very clean.
I observe revision of bios is down as on screen show A03 after change the new bios battery. Before i remember revision A08.

finally,one ram is damage. change new ram it can boot bios. Thank you.

I'm glad you got it working.  A stick of RAM going bad at the same time you changed the battery - who would've thunk.