Device Manager > Keyboards > Right click on (your keyboard) > properties > Power management tab?
If not maybe a BIOS option?
There are both BIOS level power management and windows power management/keyboard features that can affect that.
Its not something that your power button was set to put your PC into standby and tapping hte key starts it up?
On my 8.1 machine I use the sleep button on my HP keybaord, PC goes to sleep, can move the mouse about and it wont wake up till you press a key or click a button