Download Drivers For Your Camera
Go to the website of the manufacturer and select your model (this is usually done in the Support section) and see if they have Windows 7 drivers. Download the driver(s) and follow the instructions to install - every camera is different so I can't give you exact directions.
If they don't have drivers try Windows Update - Update driver for hardware that isn't working properly:
http://windows.microsoft.com/en-us/windows7/Update-a-driver-for-hardware-that-isnt-working-properly
Using A Webcam: