The hp dc models have the intel security modual built into the mother board as well as the Intel Local Management Service (LMS) and Serial-over-LAN (SOL) support for Intel Active Management Technology (AMT).
This shows in the device manager as a "simple Pci device" or maybe a "serial comm device" with a yellow! that needs a driver.
Try this one, or search the HP site for "dc7800 simple pci device win7". Use the exact name from the device manager im your search.