If you can't capture with Kdenlive then you can capture video from other applications like Kino for example. Then you can import them into Kdenlive. If you to capture video Kino then you can use the following settings as they definately work in Kdenlive.
Once you have captured using Kino, see separate manual on Kino, you can import the clips into Kdenlive. Click on Project > Add clips.
When the Open File window appears then you should select the files that you wish to import into Kdenlive to edit. If you want to select more than one then you can hold down CTRL on your keyboard. and click on each file.
When you have selected the file you want to import then you should click on Open. The screen should look a bit like the screenshot below.
Your clips are now available to work with in the project.