Recently, a user built a new gaming PC and is testing it out by running graphic intensive games. After a short time playing a game, the computer reboots with an error "a thermal event has occurred"…

An under-clocked processor would result in poor performance rather than a thermal event, since lower clock speeds generate less heat, not more.

Insufficient power to the motherboard would typically cause instability, random shutdowns, or failure to POST - not specifically a thermal event error triggered by gaming.

Hard drives are not under significant load during gaming and rarely overheat to the point of triggering a system-level thermal event, especially in a new build.

Graphics-intensive games place maximum load on the GPU, causing it to generate significant heat. If the video card cooling is inadequate - such as missing thermal paste, blocked airflow, or an undersized heatsink - the GPU temperature can exceed safe thresholds and trigger a system-level thermal shutdown or reboot with a thermal event error.