I downloaded the software and it was working fine until the techie serviced the tower. Now the mic. works but I cant hear anything. Also it keeps telling me it isnt plugged in but it is. Help

Can you see the s-mete if it has one moving up and down on any channel? Do you hear any audio at all? could be a couple of things. Bad mic switch or mic cable, bad antenna or coax, bad audio amp. To check the audio amp plug in a speaker to the PA jack, put the PA switch on PA then press the mic to talk. If it works the audio is fine the mic is good and the mic cable is good. Noiw plug the speaker into the speaker jack, do you hear anything? If not then your antenna or coax has a problem, fix or replace antenna or coax.

This is fault on the MIC within the unit. Now uninstall the driver software, remove the webcam and then reinstall the drivers once again.Now connect the web cam and open the properties settings on the webcam . check for normal settings . If the fault repeatsthe webcam must be rechecked on another PC. Take opinion to consult if the webcam is under warranty

If she can hear you - your mic is fine
The most likely cause would be her mic or your speakers - did you make your speakers default in Skype?
Vista
TEST SPEAKERS
Right click on speaker icon in System Tray or from Control Panel
Select "Playback Devices"
The speaker icon ( checked as working) and volume level graph should be visible
Right click on the volume graph and click "Test"
Left hand speakers followed by right hand should be heard

Did you try new batteries? When there's low power, the mic will cut out. You should keep fresh ones in there to be sure.

A webcam is a piece of hardware, you cannot download it. If it's installed, it should work fine. If you cannot hear any sound, try checking your audio settings, via control panel. There may also be some problems with your webcam software settings, which you can look at when you access the software. Good luck.

try using the windows sound recorder in the accessories menu in the all programs menu in start menu
if you are able to record sound on that it means that your mic is fine but the game or software your are using to communicate to your friends doesnt have it selected
if the windows recorder doesnt work with your mic then either the mic is broken or it is not set as the default sound recorder in windows sound settings

It could be possible your phone mic is out of order.
So you should replace a new mic and if your mic is good such as your phone recorder is work properly then you should install its software.
Good Luck

there is a speaker socket behind the tower

Try and redownload the driver. 
heres a site youd need to find it if you dont have the cd
http://www.logitech.com/index.cfm/support_downloads/downloads/&cl=us,en?selectedcrid=408&selectedcid=221#

may I ask u how long have u had this mic because I had mine for a while and this recently started to happen to me and because of the updates sony has been releasing I believe thats the cause because mine didnt start doing that until update 2.41 was released