While there are many things that can be an issue, and despite many patches Windows power management is still buggy, one that seems to help is to open your power option control panel, click "change plan settings" on the plan that you have selected, then click "change advanced power settings." Under PCI Express, Link State Power Management -- turn that setting off.
If you have a USB keyboard and mouse, it also may help to not let those device controllers power down:
Open the device manager, open the Universal Serial Bus Controllers, and for the USB Root Hub right click and select properties -- then the Power Management tab. Uncheck the box "allow the computer to turn off this device to save power."