First of all, make sure your host is easy to use, right? Generally, the method to test whether it is working is very simple, which is to turn on the computer and plug in headphones or speakers. If you can hear the sound entering the system, it means there is no problem with the host. If there is no problem with the host machine, then after the machine is turned on, the display will first have a green light and then turn to a yellow light, which means the following points:

1. First, do not connect the signal cable (that is, do not connect it to the computer) and see if there is a LOGO screen on the monitor ( It is the trademark of the monitor) If there is a LOGO screen, but it just flashes and then disappears and then the indicator light turns yellow, then it means there is a problem with the high-voltage board or the lamp of the monitor. If there is a LOGO screen and it is displayed for a long time or it shows no signal connection, it means there is no problem with the monitor.

2. If you can display the LOGO screen without connecting the computer monitor and prompt that there is no signal connection, but after you connect it to the computer, it first turns green and then turns to yellow, then you need to check the VGA signal line of the monitor.

3. If your monitor has two data interfaces, one is VGA interface and the other is HD interface, then your monitor has a switch key between VGA and HD.

4. You take the machine to the computer maintenance department, and the inspection shows that there is no problem, but I don’t know how long your complete machine has been ordered in the maintenance department, and whether the set of your original machine was used when ordering. When connecting cables, sometimes the monitor click time is short and the problem does not occur.

5. Another possibility is that sometimes the machine's graphics card will have a VGA interface that is easy to use, but a HD interface that is not, or vice versa.

6. Your question is not comprehensive. For example, does the indicator light on the monitor turn green and then turn yellow when the device is turned on? Does it take a while for such a problem to occur? Or does it occur after a period of use? Also, what did you think when you took it to the computer maintenance department to see it?