Microphone not working

I have an Inspiron 1721 with Window's Vista.  Although I have the input jack for a 3.5 mm jack, I can not get the microphone to work.  It also seems that I have no information when doing a search, or even working in the control panel.  This is a new computer, and I need the microphone so I can add voice to a project I am working on.  Any specific help would be great.  Also, please dont tell me to go out and buy a new mic set...I've had the same Mic for 10 years, and all has worked great, regardless of computer maker or operating system....  Help!  I am dependant on my microphone for my business and it's success!  Without it, I  might as well flush the computer down the toilet....