Windows doesn't always like going to sleep. This has to do with the motherboard and interface cards that are sometimes in conflict. Problems usually occur in Sleep mode and upon waking up. It happens often to Audio cards and Video cards where it seems to freeze up.
I know the USB port gave me a problem with my mouse at one point. The secret is to go to the DEVICE MANAGER settings then one by one, double click on the "USB Root Hub"
Go to the POWER tab and check if there is something using power (a device plugged in) If it says that the "Power Required" results in 0 mA, then there is nothing connected to that hub. Go to the next USB Root Hub and keep checking the power tab. For my Keystep device, it says that I have a "USB Composite Device" using 100 mA. The same goes for my Keylab Essential 49 (100mA). To double check, unplug your device and do a refresh. If it disappears from the list, that's the hub it's connected to.
Plug it back in then click on the "Power Management" tab and see if the "Allow the computer to turn off this device to save power" is checked. If it is, try to uncheck it then try again to see if the problem re-occurs. If it solved the problem... Good.
For the mouse, I needed to check it in order to stop my mouse from wakening my computer whenever it was moved.
Good luck.