My laptop doesnt recognise my in-built microphone (Advent 7115).

Hi
I have an Advent 7115 laptop with an in-built microphone, runnning on Vista.

I have already used the in-built mic a couple of weeks ago to talk to my parents on Skype. It had a good range (I was sitting at the table talking normally to my computer). Last week I tried to use it again and I had to be right against the mic and speaking very loudly into it to be heard at the other end. I tried it a couple of days later and Skype informed me I had no microphone.
I checked it in the Sound part of the Control Panel and it said there were no microphones detected. I tried an external mic with a jack for the mic plug (i.e. not USB) and that isnt recognised either.

Can anyone help me? I don't know what to and I am not very technically able with computers.
Thank you