Computer can't find Wi-Fi connections?

I moved and in the old apartment I always had good internet with the computer. I also have good internet in the new apartment, e.g. Via my laptop, but my computer can't receive any Wi-Fi. The symbolism is the Wi-Fi sign with a red cross on it. The strange thing is that he does not receive any Wi-Fi at all, not from the neighbor or anything.

Does somebody has any idea?

Counter question: Is your Wi-Fi on at all?

I have already made sure of that. Normally everything would have to work, but the computer can't receive a network.