Why won't my computer even boot a bootable flash drive?

Question

Iron

After starting the computer, it does a self-test for 15 seconds and the cpu, dram, vga, boot indicators light up in turn. But at the end, the boot indicator does not go out and the computer starts up and gigabyte is shown on the screen and you can enter the BIOS. If you do not go into the BIOS, then the computer starts rebooting and all over again. I checked the video card, power supply and ssd disk on another computer, they work properly. In BIOS, the disk and flash drive are visible, but when you choose to start from a flash drive or disk, the computer restarts