Microphone Icon

I hope someone can help me here.
My Microphone Icon is suddenly not working.

I have a Dell with WinXP that I bought a year ago.
Last week my Microphone Icon suddenly is no longer working, and says
the problem must be with the headset. I tried again and again to get
it to work, but with the same answer.
I retested my Logitech headset per its instructions, and it is working
perfectly fine. So it's not the headset. It was working with it up to
now, no problems.

I have no clue what is going on here, and why the Microphone Icon
won't cooperate with a perfectly functioning Logitech headset.

I hope some kind souls here can help me out.

Thanks, Hal