My sister has a laptop, she says it cuts out frequently (the fan turns off and the screen goes black). I've never had this when I've used it although I have noticed the fan is noisy and the laptop gets very hot, it feels very warm on the keyboard. I've had a look at the fan and there doesn't seem to be much fluff so I'm thinking it's the fan and I'm tempted to replace it.
My only concern is that it if the systemboard controls the fan it might actually be the system board that's faulty. Just after a second opinion really,