For USB connections:

• Right-click My Computer and select Properties.
• Click tab Hardware, click button Device Manager.
  • Expand Universal Serial Bus controllers.
  • Double-click USB Root Hub (or right-click it and select Properties).
    • Click tab Power Management.
    • Uncheck Allow the computer to turn off this device to save power.
    • Click OK to exit USB Root Hub Properties.
  • Click the “X” to close Device Manager.

For ethernet connections:

• Click tab Hardware, click button Device Manager.
  • Expand Network Adapters.
  • Double-click specific Network Card.
    • Click tab Power Management.
    • Uncheck Allow the computer to turn off this device to save power.
    • Click OK to exit Network Adapter Properties.

Click the “X” to close Device Manager.

Additionally, try checking the Susfail.txt found in the %systemroot% directory.

For additional documentation:

http://support.microsoft.com/?kbid=232728