Make sure you do not have Windows USB port power save option turned on.

Turning off a USB port’s power save option on Windows XP Pro

  1. In Windows, click on Start >Control Panel (or Start >Settings >Control Panel).
  2. Double-click on System, then open the Hardware tab.
  3. Click Device Manager.
  4. Click the + at Universal Serial Bus Controllers.
  5. Right-click USB Root Hub and select Properties.
  6. Open the Power Management tab.
  7. Clear the checkmark from Allow the computer to turn off this device to save power.
  8. Click OK.
  9. Repeat this procedure for the USB 2.0 Hub.