Hello can anyone please help.

I have an optiplex 7010. For years I have run a small monitor using the VGA port. 

Recently I bought a new monitor that doesn't have a VGA port. But it does have a displayport.

Once it has booted the new display port monitor works perfectly

BUT I cannot display the bios settings on the DP monitor. No amount of key pressing will get me into a screen that I can see. This works fine on my old VGA monitor. But not on DP. 

Can anyone please tell me how to see the bios using my DP monitor?

Many thanks