Usually, I recommend a system restore using the recovery CDs that are available for your computer but the process is a little complicated and involves losing installed applications in your Program files folder. Instead of that operation, a better approach is to perform a reinstallation of the drivers available.
I have performed related search queries for your laptop and found the necessary drivers that will work. Please, use the Add or Remove programs section in your Control Panel, and remove everything related to Dell Webcam (Note: Do not remove Webcam Central, if you have it installed). After this operation download the new driver package and perform a fresh installation, then perform a restart of your computer. You will notice that the next time you use Skype the camera will work as it should.