(2) The motherboard has no power supply;
(3) The graphics card is poorly contacted or damaged;
(4) 4) Poor CPU contact;
(5) Poor contact of memory stick;
(6) The machine is infected with CIH virus and the BIOS is destructively refreshed;
(7) Check the plugging and unplugging, and remove the oxide film on the golden finger with rubber if necessary;
(8) If there is a floppy disk in the floppy drive, it will often lead to a black screen when the computer is turned on or restarted, and it is impossible to enter the system. In order to avoid this situation, you can also cancel the floppy boot entry in the BIOS.
In addition, you can unplug the graphics card, wait for a while, clean up the graphics card slot with a brush, and then plug it back in 5 minutes. I hope I can help you.