I have assembled a new computer and this problem has me stumped.
Background information: A USB connector has four “pins” in line. The two outside ones are a bit longer and make contact before the two inside ones. The two outside ones carry the supply of zero and +5V and the two inside ones carry the data. Additionally there is the exterior metal housing which is connected to ground for the purpose of shielding.
The problem: The mainboard has two USB ports on board and a header for two additional ports off board. The case I have has two USB connectors in the front connected with flat cables to the USB header on the mainboard. When I connect a device to the USB connectors placed on the rear of the case (directly on the mainboard) everything works fine but when I go to connect a USB device to the connectors in the front, just when the shield touches the shield, and before any of the main connectors touch, the computer resets itself like I had pushed the reset button. It does not happen every time but it happens often enough to be annoying as I have to wait for scan disk, etc.
When I started looking into this I noticed the shield of the USB connector was grounded through the 0V USB pin to the mainboard. I thought some static might be enought to send something through the mainboard so I disconnected the shield and connected it to the chassis a couple of inches away. And it still does the same thing! Touch the USB connector shield with a metal object (not any of the four pins) and it often resets the computer. Touch the screw two inches away where the USB shield is grounded to the chassis and nothing happens. It makes NO sense.
When I had the computer without proper grounding it happened a lot. I have properly grounded the case an it happens much less but it still happens ocassionally. It has me completely stumped. The only thought I have right now is to replace the USB connectors in the front of the case with connectors in the rear which would have shorter cables. Anyone have any other ideas?