Apparently whatever you are connecting to the POWERED USB port [it the powered port is mandatory], is something that draws considerable current from ther 5 volts.
If you connected the device to the powered hub, but DID NOT have the hub power adapter plugged in, the device may have drawn too much current from the 5 volt USB connection within the computer. This may have caused the computer shutdown. The amount of current required for the device certainly shouldn't be too much for the main 5 volts from the Power supply, however, the computer's USB circuits may have built in protection to prevent getting burned out by overload. [of course, it is possible that the device has failed and is shorted]
This is simply a WAG, because I see that no else has answered for quite a while, although on summer weekend days many people that normally reply are enjoying something else.
I am not absolutely sure what device was being connected. Possibly a little more precise explanation of what you were doing step by step would clarify it further.
I mistakenly fouled up my broadband connection on my home wireless network when I was trying to clear some space to install Norton Systemworks Go Back. When I reinstalled the software, it said that I should not have the network card attached to the computer during installation. I dutifully disconnected the unit. When it got to the place where it says to connect to a powered USB port, it did nothing when I plugged it in to the USB port on my USB hub, the port from whence it came originally.
I then tried plugging it in to the one free usb port on the computer. The whole computer shut down. Instantly, like I'd pulled the plug. I checked that everything was plugged in properly, started over, and the same thing happened when I plugged into the computer's USB port. It all worked ok yesterday.
Gateway desktop (Bought in 2000. Several hardware upgrades since then,including DVD drive and 80 gig second hard drive.)
XP professional OS
The wireless network is MSN. Base unit is on my son's Dell, which is tne newest computer in the household.
Any help would be much appreciated. I tried reaching Gateway's tech chat, but it throws me back to the desktop when I try to connect. (From my son's computer,not the one with the problem, natch). Thanks