Don't bother with regcure!
it will tell you you have x amount of faults and try and get you to pay for it to "cure" them when in reality there are no faults that need anything done to them.
it's highly unlikely that it's anything to do with the registry that is causing your mic problems, its much more likely it's simply muted.
Double click on the little speaker icon down by the clock, when the mixer comes up click on the file options menu and select properties, then click on the recording tick box and click OK, you should now see the input controls for your sound card, make sure that the mic is selected and turned up and click ok.