My Phone Won't Respond

I was using it normally, then pushed the button on the side for it to be in sleep mode. I got a text, and went to check it, but the screen would not turn on. I tried turning it off, but it would not work. The only thing that worked was taking out the battery then putting it back in. This is the second time this has happened. Any ideas?

Please explain in detail. I'm also using xperia sl. I don't have that problem.

Mary doe,
As far as i know, the xperia sl has an inbuilt battery. what do you mean by taking the battery out and putting it back in?
I use an SL. So kindly let us know so that we can be of help to you