Simulink doesn't let me connect blocks

I'm facing a big problem with simulink. If i want to connect for example a step with a normal black line it doesn't let me do that. How can i do? The problem is the same for every block, when I want to connect the output of a block to a black line, I can't !!!! Please help me, I'm desperate. I've tried everyhthing, i've also reinstalled matlab two times, but the problem didn't vanish.

Let me show you with a figure..

Answer 1

[Azzi Abdelmalek]

You can't connect a signal to a signal, but you can connect a signal to a block.

What do you want to do with these two signals? sum? product? or what?