There are several things you can try, in order to restore the functionality of your webcam on Skype. First of all, check your webcam's availability at the following link http://www.testmycam.com/ After that, try the following solutions.
For Windows OS, go to this page http://process-explorer.software.informer.com/ and download Process Explorer. Open the application, hit Find and Find Handle or Dll. A window should appear, in which you have to type #vid and click the search button. This will allow you to see the list of applications that interfere with your webcam. If the search returns empty, no application has your camera in use. If the search returns a list of results, analyze each of them and kill them one by one, until you restore your camera's functionality on skype. Most likely, this problematical application is being started by your system. To check this theory, go to Start, Run and type msconfig. From the newly opened, go to Startup tab and deselect the desired software, hit Aplly and OK.
If this isn't working, go to Start, select Run and type regedit in the blank box. From the available sections, select HKEY_LOCAL_MACHINE, SYSTEM, ControlSet001, Control, Class and{6BDD1FC6-810F-11D0-BEC7-08002BE2092F}. From the left panel, choose UpperFilters and add ksthunk line if it's missing, by selecting New and Multi-String Value. Name it UpperFilters and reboot your computer.
For Mac OS X, the solution is simpler. You just have to close Skype, go to /Library/Quicktime/ delete the CamCamX5.component, open and login Skype.
