does not seem to be an exact art with any Windows machines, and many people seem to have problems.
It is best to shut down each night if the computer is not being used, and disable the stand by settings.
I always put my computer in stand-by mode at night. When I try to get back on the next morning it will not come out of stand-by. I can see the CPU light, but it will not bring the monitor out of sleep. I have to turn CPU off and start over. Need a clue.