Make sure your USB controller isn't using the same IRQ as anything else. If it is, that could lead to the instability issues you are describing.
You can check by opening Device Manager and viewing
"Resources by Connection".
To open Device Manager, click Start, then right-click "Computer" in the Start Menu. From the menu that appears, choose "Properties".
A window opens. In the top left are a list of 4 tasks. Choose the one at the top that says "Device Manager". The device manager opens.
Click View, then choose "Resources by Connection", as shown.
See the screenshot below for how to use Device Manager to check the IRQ your USB controller is using:
As you can see, on my work PC the USB controller shares an Interrupt Request (IRQ) with the IDE controller. This does not cause any problems for me because the USB devices I use are a keyboard, mouse, and backup drive, which all have relatively low bandwidth requirements. However, if I were using a Virus on my USB port on this computer, it is likely I would run into problems.
Unfortunately as IRQ assignments are generally left up to ACPI these days it's a bit tricky to change them to something else. Here is a link that describes a similar problem, with steps for resolution on the 3rd post down.
http://www.techspot.com/vb/all/windo...Q-numbers.html
Hope this helps!
-Annikk