I don't think there was one European language before IE. Most likely South was speaking Afro-Asiatic/Semitic form brought with first farmers, mostly J2 people, as with E, T and J1. HG I people, hunter-gatherers from North, were speaking some old language, but who knows what? Most likely we can vaguely speculate about 100 words of that origin. We did this exercise in some other thread, but I can't find it at the moment.
There was also long and strong influence of HG G, most likely from Caucas, and who knows what they spoke in Neolithic?
Invention of time machine is highly necessary in this case!