Why does my Xbox turn on by itself?

So I've had my Xbox since the 1st Halo was released. It has been working fine up until about 2 years ago. I woke up one morning to find it was on...I first thought that I must have thought I turned it off but didn't. When i hit the power button to shut it down, it wouldn't turn off. After a few attempts at using the button, I decided to pull the plug. Later, I plugged it in again, and it immediately turned on. I pulled the plug. Then a few days later, I plugged it in again, and it seemed like everything was normal. I hit the button to turn it on, it turned on, then I hit it again to turn it off, it turned off. A few hours later, it turned itself on again. And so since this first started, this is how it's been behaving. Most of the time it wants to be on, so I have to pull the plug to turn it off. But there are those times where it will act normal. I'm under the impression this might be a power board issue, but I would like to get some feedback on this before I attempt to fix.