Spanish accents

Hi,

I used to be able to add accents in to my documents when I would type (Macbook air). I would basically just hold the key down and select which accent I needed, however now for some reason it doesn't do that anymore and looks like this instead: nnnnnnn, or aaaaa, eeeee, etc.

Have I pressed something by mistake or is there anything I can do for it to go back to normal?

Thank you :)