1. The question. This should be, for example: Do these have the same meaning? Do these mean the same? 2. The answer. Only the first sentence is correct. 'I couldn't speak.' is correct. It means that you weren't able to speak at some point in the past. The other sentence is simply wrong. The form doesn't exist.

I speak. I am speaking. I spoke, I have spoken are the present and past tense forms of the verb to speak. I could speak, I will speak , I might speak I won't speak, I couldn't speak - you can see here how you use "speak" as a participle.