as per hp site:
"Although the HP Compaq 8200 Elite Small Form Factor PC has no rear chassis fan installed, this error message may arise when the front panel cable assembly was damaged after a system repair attempt.
In a HP Compaq 8200 Elite Small Form Factor PC, Pin10 on the front panel cable connector is used to tell the system BIOS, that the chassis is a Desktop model, not Microtower model. This is necessary because the system board is also used in HP Compaq 8200 Elite Microtower PC, which has a rear chassis fan installed. Pin10 is not connected there.
If the cable on Pin10 of the connector in a HP Compaq 8200 Elite Small Form Factor PC was damaged accidently and therefore has no connection to the system board, the BIOS assumes that it is a Microtower model and therefore checks for a rear chassis fan."
There is a problem with the front panel connector:
Let's remove it and look, the pin 10 is not connected while pin 5 (usually unused) it is:
We just need to remove the plug from pin 5 and move it to pin10:
Finally the ground is moved from pin 5 to pin 10: