I have an Acer and you'll have to press Fn + the numlock key (numlock is written in blue letters).
Then your problem should go away.
The problem is easy to explain, most Acer laptops (and others) don't have a num-pad.
Instead they have a num-pad integrated in their keyboard.
J = 1; K = 2; L = 3; U = 4, etc.
It might have happend that you accedently turned it on.