I seems to be related to wall outlets in my house. It fixes itself after some days or weeks and them it starts again. I am frustrated on not knowing how to fix it myself or what is really causing it. I have done all resets, safe mode, checked hardware (it is fine), etc..etc...
I have to shut down using power botton every time.
MacBook Pro (13-inch Mid 2010), Mac OS X (10.6.8), Snow Leopard