Hey guys, I recently upgraded my PC and ran across a very strange problem... My mainboard is an Asus P5Q that has 6 USB ports on the back (in groups of two). So far, I attached the keyboard and the mouse to the first "block", a webcam and a Seagate FreeAgent 1 TB USB disk to the second one and a printer and USB hub (built into my display) into the third one. When I turn on my PC, the BIOS recognizes...

1 keyboard, 1 mouse, 1 storage device, 1 hub

Since I think it cannot do anything with the printer and the webcam, so far so good. However, once Windows boots up, I get an error that an USB device does not function correctly and the device manager tells me that an Unknown Device listed under USB cannot start. What doesn't seem to work is the printer and the hub. If I remove the two devices and attach an USB storage device, I get the same error: a device attached to this computer does not function properly. Because of this, I frist thought that the mainboard might be damaged and was just about to RMA it when I noticed something very strange: when I boot the PC with the HDD unplugged, everything works perfectly. Once Windows boots up, I can even attach the HDD and everything continues to work perfectly fine. The USB HDD has its own power supply being a 3.5" unit so I guess it's not something related to the power. Any ideas what might be wrong here?

Is it possible that the drivers of the external HDD haven't been installed properly (or possibly at all) and this is resulting in the system failing to recognise it?

Have you tried swapping which ports each device is plugged into? You may have some luck doing that.

No, the HDD is recognized as mass storage device by Windows and the native drivers are installed automatically. Anyways, it's not the external HDD that is not recognized, but other devices connected to the same block (pair of USB ports), be it the webcam, the hub, the keyboard, the mouse, the USB headset, etc. which all function properly if the external HDD that I repeat is connected to another USB port is unplugged when powering on the PC.

Uh, what system??

What exactly do you mean? It's an Asus P5Q board. I never managed to solve the problem, but am using a workaround - the webcam and the printer are now connected to the display USB hub so I can easily take the webcam and use it with my notebook in case I need it; same applies to the printer if I want to print something from the notebook so I don't have to dig for the cable beneath my table. Works so far. I also replaced the USB cable of the HDD with one that is a. shorter and b. contains something like this:

So the problematic detection only for devices connected to the same block?

I strongly suspect it's a power problem; somehow the external HDD's power interferes with the USB block's power, resulting in not enough power being delivered to the other device. The external HDD, having its own power supply, doesn't care because it can still inject signal into the USB datalines.

Try plugging the external HDD *unpowered* and see if the other device is detected or not.




Ahhh... a ferrite. Used to absorb noise
Nice cable that. How much did you pay for it?