System is not detecting Mic

[Shilps]

am not sure if anyone else has faced this problem before, but I first faced
it with Dell Inspiron 6400 and now I am facing it AGAIN with Inspiron 1520
..The problem is that system starts working fine, but after some time it stops
detecting headset mic on a random basis and then completely stops detecting
it.

With Inspiron 6400( Os Vista Home Basic), when it randomly stopped detecting
the mic( I use it for voice chat on Yahoo), I used to re-install the driver(
SigmaTel) and it used to work fine but the problem would recur after a
shutdown.Again the same cycle. Then one fine day it completely stopped
detecting the mic even after doing re-install of OS itself !!

Same problem I am facing with Inspiron 1520( OS Vista Home Premium).

I am not sure whether its a problem caused by Updates which is set to
Automatic( if yes, then which update) or is it being caused by some software
installed.
I have a suspicion that it might be due to Noika PC Suite, but I am not
sure. I uninstalled it, it worked for 2 shutdowns, but now again it is not
working.

If anyone has any clue pls let me know. But the problem is that for 6400, it
didnt work even after re-installing of OS and now suddenly these days, its
working fine. I have gone nuts trying to resolve this issue. Dell has walked
off saying its an OS issue, we can't help you in anyway.

I ran diagonostics and the system is detecting the mic. It has to be because
I am testing with 3 different mics and all of them are working smoothly on
other laptops/desktops

What do I do?

TIA
Shilps

 

[Shilps]

Just wanted to add that I am checking the mic with Sound Recorder and Control
Panel> Speech Recognition and Yahoo.