A user built a new PC with parts sourced torn a popular online vendor.

Thermal paste is a substance that fills in any gaps between a CPU and its heat sink, which is a device that dissipates heat from the CPU. Without adequate thermal paste, the CPU may overheat and cause the system to shut down automatically to prevent damage. This is especially likely when running 4K video or games, which are more demanding and generate more heat. The technician should check if the CPU heat sink was attached properly and apply enough thermal paste to ensure good contact and heat transfer. Reference: https://partners.comptia.org/docs/default-source/resources/a-core-series-combined-content-guide (page 28)