Hi, thank you for contacting JustAnswer.com. My name is Russell. I will do my best to provide the right answer to your question.
That sounds like a case of the device being accessed by two different programs at the same time. Or perhaps just a simple case of (a trifling amount of) computer overload.
1. try closing, and stopping, all other program windows, before making the Skype call.
Or as many as possible.
2. make sure especially that any program that might access or 'poll' (i.e. signal to, or check on) your video facility or camera, or your sound card even, is definitely completely stopped and exited, before you start your Skype call.
After that... if that doesn't help... it's two more questions:
A. do you perhaps have a virus on your system? they can be badly (if not also rudely) programmed, and 'break in' to other programs and activities.
B. do you perhaps not have enough RAM installed on your computer? let me know, what you find out and what happens, and I will advise you further.