Hi Amata,
1. No file attached to try to check.
2. No output appears means probably the signal is blocked or not calculated at certain point. So I suggest you to trace the component step by step to catch the congested point, where the signal disappeared there
3. Particularly, if you can not connect two ports that means they might provide different signals types like you are trying to connect electrical signal to optical one for example. So make sure of the ports that you are trying to connect!!
Hope that helps,
Mohamed Abouseif
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