Finding a specific physical manual for OEM motherboards like the Lenovo IS6XM Rev 1.0 can be difficult because Lenovo does not typically release "do-it-yourself" style manuals for these boards. They are proprietary boards manufactured for Lenovo (often by Intel or ECS) specifically for their desktop towers (typically the ThinkCentre M-Series, such as the M800, M900, or M910s).
This board relies on the APU (processor) for graphics. If your processor is an Athlon (which has no integrated graphics) and you have no dedicated GPU installed, you will get no video output. Lenovo Is6xm Rev 1.0 Motherboard Manual
Thermal Header (THER_HD): A dedicated 2-pin or 3-pin header intended for an external temperature sensor found in ThinkCentre cases. Finding a specific physical manual for OEM motherboards