What kind of webcam are you using? If you can give the exact model you will probably get a more detailed answer. Normally with a webcam you just plug it in and it works, but there may be special problems - for instance, if you look at this page you will see examples of questions and solutions for one webcam. If you type your exact make into a search engine and add 'turn on' you should be able to find a more detailed answer.
Mine didnt work either it kept on telling me that I had no web cam and that I had to connect one because of I don't know what error.And when I try to set it because it asks me if I allow the website to view my web cam I click allow and they still don't let me.My dad is really good in computers and he told me that you have to restart the computer but if it doesn't work then try to remember if you clicked any buttons or if you went on a website that blocked your hole computer,if so you have a virus and your camera is basically dead if it works congrats if not you need to go to a repair store and fix your camera but with that money you could just buy a new computer so it's up to you.