I have created a Flex project in Flash Builder 4.5.
Next I added fl.controls libraries (and then mx.controls libraries) in the project.
I am adding a screenshot so you can see the setup and the code.

However when I run/debug it, nothing appears in there. Totally white.
I’ve worked with fl.controls before, I used Flash CS5 to compile the ActionScript project and they worked correctly.
Is there any particular reason why it does not work in Flash Builder?
UPDATE: When I add graphics to the text input, i.e.
ti.graphics.beginFill(0xFF0000);
ti.graphics.drawRect(0, 0, 100, 30);
ti.graphics.endFill();
I do see a red rectangle shape. But still no editable text input box. I tried setting ti.editable = true but no use.
Try this:
Create a new FLA in Flash Professional. Add the TextInput component to your library. Notice that not only does the TextInput class get added to the library, but also a folder of “Component Assets” – skins and such. Flash Professional components are not just code – they are code and graphics.
If you want to use fl.controls.TextInput in Flash Builder, you can publish that FLA you just created with the “export swc” option checked. Include that swc in your Flash Builder project, and you’ll be able to instantiate the TextInput in your code. If you want to add other Flash components, add them to the library in the FLA and republish the swc.