if you have a USB mouse/keyboard and you upgraded from windows 7 your system might be powering down your USB hub your mouse/keyboard is connected to. You might boot into BIOS and look in the power management section and tell it how you want to wake up the machine, and tell it not to power down your USB hub.
You might also have your devices plugged into a USB 3.0 port that does not have the proper driver installed.
In that case, try using a USB 2.x port for your keyboard, and make sure your BIOS is set to wake up the machine with a keyboard "space" key (that is what I use anyway)
Also, depending on the year your machine was made, there are lots of bugs in the BIOS related to USB ports.
2009 BIOS had lots of bugs in the USB 2.x...