I have DELL M1330 notebook with USB 2.0 ports in which I plug a Kensington 8-port self-powered USB hub. Since recently, the devices disconnect almost at random. Some events seem to trigger it, but it happens spontaneously as well. For example, when I plug in a device (HD or PDA) then all the lights on the USB hub go out and none of the devices work anymore. An exanple of no trigger causing the same effect: sometimes I leave the computer running at night but when I move the USB mouse in the morning, it has been disconnected and I need to use internal touchpad instead. There is another non-self-powered 4-port USB hub plugged into the other hub btw, but the devices connected to this one are usually off (they're self-powered external HD's).
The 8-port Hub seems to be listed in Vista as two "Generic USB Hub"s with 500 mA per port available. The other 4-port Hub is listed as such with all ports still available and it "has a single TT" (I'm not sure what that means)
Does anyone know what could be causing this?