Keeps turning on

I have my pc set to sleep I in a half hour, it goes to sleep the monitor shuts down but then maybe and hour later the pc starts up the monitor dose not come on and ina couple of hours it dose it again, why

 

Could be one of several legitimate reasons. Windows Update may be downloading an update. Your security software may be scanning. Windows may be doing some "housekeeping" chores.

But there could be other things waking it too. Even things like heavy footfalls, big trucks or jet engines can wiggle a sensitive mouse enough to wake a computer up. Or it could be another computer on your network pinging this computer's network adapter.

See How to Find Out What Woke Up Your Computer Last.

 

I don't think it updating as its been doing it everyday for a while, no vibrations as the happens at night also not a busy place