not all systems came with a build-in mic

are you sure yours has one? ours does not. so my simple solution is to buy a cheap web camera (all-in-one with a mic) for below $19. the software install is quite easy, just place the CD-ROM (came in the same package) in the CD drive and follow instructions.once it's done, plug the cable in a USB port, that's it. skype should be able to detect them all. good luck!!