When the computer is turned on, the fitness light will flash black.
1. It may be that the signal line of the monitor is not connected properly. Check the signal line again to make sure that the monitor is turned on.
2. There may be too much dust in the chassis, and there is a problem with memory identification. Open the case, remove the dust, remove the memory stick and wipe the dust, preferably with a hair dryer. Then install and open it.