How to disable mic??

[Acerpizza]

Hello
I have an Acer Aspire and I am unable to turn the mic off. I have connected it to an external amp in order to play music from it, but it feeds back as, although I disable the mic, it doesn't actually turn it off.
Any ideas folks? Thanks

 

[Acerpizza]

I've sorted it - even though the mic was disabled I still had to mute it. The option to mute the mic is under SPEAKER levels!