Check the ESD protection diodes near the rear USB ports. A short here can trigger the Power Supply Unit (PSU) protection mode. Finding and Reading the Schematic
Detailed pinouts for specific headers, such as the front panel audio and CMOS reset jumpers, are documented on technical viewer sites like 2. Motherboard Architecture (Ver 8.0) The H61MGV3 Ver 8.0 is built on the Intel H61 Express Chipset and supports: h61mgv3 ver 8.0 schematic
Repairing the Biostar H61MGV3 Ver. 8.0: Schematic & Troubleshooting Guide Check the ESD protection diodes near the rear USB ports