Hello Miss Paula,
It is not as simple as just adding more ram to a computer.
What you need to do is check the speed of the memory that was in the machine in the first place. All the information of the memory sticks should be found on a little sticker on the memory stick.
You need to take note of these, because if you buy some more memory it has to match the old set of memory sticks. The end result is likely the new memory does not match the old memory, So it is why the Lights are on but no one is at home as you say.
You also need to check how much memory the motherboard or laptop can access in memory size.