HP Service Centre Contact Center

I don't know why and how long this has been going on but for some reason i can't turn off my pc, there's nothing running in the background, i did a full system scan with norton results are clean, i just don't understand what's happening. First i turn off the pc by clicking on the shutdown on start then it shutdown like normal but after the blue background it turns black and that's the last part where it should turn off but when it turns of it just turns on back again. The only way for me to turn the laptop off is to hold down the power button which is a bit annoying because when it restarts or i turn it on, i get sent to a black screen with words giving options on what to do, to start up windows.