sound input problem

[dipsibar]

Hi

Hope somebody can give me some advice with this.

I have a problem with the sound input on my emac which has only appeared (or disappeared) since yesterday.

I went to call my mum on Skype and found I couldn't hear her. I then went to system preferences and sound and saw my option to use the built in microphone for my sound input has disappeared. It's been there for the last 9 months but now it's gone and the only option is "Line in".

The sound is otherwise as normal.

I would be extremely grateful for any advice.

Kind regards

DP