hmm....i was not pretty sure about it, it was my friend laptop, he's in s'pore rite now. And, i don't think he dare to remove the memory and take a look on it, he doesn't know much about laptops i think.
But anyway, i did purchase a new memory stick for mine, and it works. So, maybe it's the memory stick's problem, and he told that the manufacturer promised to give him a new one later.