My sister's laptop has some sort of weird problem. Sometimes, when you run it for a while, it just locks up completely. After soft powering it down, it doesn't always boot up again. Pressing the power button causes the status light to pop on, like usual, but then all that happens is the Caps Lock button flashes on and off for a while. Sometimes it will turn on, but running it even for a little bit causes another complete lock up.

Any advice?