Have a look at this [link|https://www.youtube.com/watch?v=omYY8fly2pE|guide] for replacing the key caps (volume off) or [link|https://www.youtube.com/watch?v=Zwk3q6Tbflw|here] or [link|https://www.youtube.com/watch?v=EHpb2UR5slk|here] depending on model and keyboard types. Hopefully nothing has broken which is making the key appear to be stuck down. (There maybe a small rubber thing that goes in the center that pushes the key up, I have a feeling that is missing.