On the MH61R, look for a header labeled or simply FRONT PANEL . It is located near the bottom right edge of the board, usually just above the SATA ports.
If you are reading this, you have likely just experienced a specific flavor of PC building frustration. Dell Mih61r Mb Front Panel Pinout
You have a Dell OptiPlex 3010, 7010, or 390. The motherboard is the (often labeled CN-0Y8H8Y or similar). You decided to move this motherboard into a standard ATX case to save money, or perhaps you are trying to diagnose a power button failure. On the MH61R, look for a header labeled