Problem: An HP ProDesk 600 G1 computer will not recognize a monitor connected to the DisplayPort via a DisplayPort adapter.
1. Update the video driver from the HP website
2. Update the BIOS
3. Clear the CMOS (power off the computer, unplug the computer, hold the CMOS button on the motherboard for 5 seconds)
4. Use an HP DisplayPort adapter - I have specifically observed certain 3rd party DisplayPort adapters that refused to work with a ProDesk 600 G1 even after performing the above steps, just to have things work when I used a different brand of adapter. So if you need to, just order an HP brand adapter.