What kind of computer do you have? Any idea of of the wattage of your power supply? How many other peripherals or bits of hardware are plugged into the computer (keyboard, mouse, printer, USB hub, etc.)? Do you hear a beep when it shuts down? Typically, when a PSU spreads itself too thin it will shut off as a safety measure. That's why when troubleshooting PSU's you're supposed to disconnect peripherals and other internal components piece by piece to see if the computer will run better. So, that's my vote. If you find now that your computer keeps shutting itself down WITHOUT the passthrough, the PSU might be damaged.