On my first batch of Dell Precision 490 Workstations, users complained that if the machine went to sleep or screen saver that it could never come back up. After I placed a call with Dell the problem is the result of a new feature that turns off USB devices to save power. The feature is enabled by default in the BIOS but I will disable it manual in Windows.
First open Device Manager and scroll to the bottom section called Universal Serial Bus Controller. You will need to right click and go to the properties of every “root hub” section. On the Power Management tab you need to uncheck the “Allow the computer to turn off this device to save power”. The new feature is now disabled.