Fault diagnosis
Answer a few questions to narrow down the cause. The steps follow the order technicians actually use: rule things out from the outside in, from cheap to expensive.
Try the monitor on another display port of the machine — any picture?
Industrial PCs usually have 2–3 display ports. Switching ports rules things out very quickly.
Before opening the machine. Disconnect power, wait for capacitors to discharge, and photograph the current wiring. If the machine is under warranty, call us first — opening it yourself may void the warranty.