Antivirus problem on my aunt's computer?

My aunt's computer has a reoccuring problem where she will be in the middle of something, and a blue screen appears saying something about an attack has been found on her computer, and it says dumping memory. It happens all the time though, she doesn't even have antivirus software. All she does is play on neopets and pogo. How can we stop this blue screen from popping up all the time?