Wifi access

Question

I have an acer extensa 4420 and I can usually recieve a signal for wifi and surf the internet. I have tried to access a signal that is 78percent and higher and my computer says it cannot connect to this signal. I checked to find that the network is not a secured one and it says that I have manually disconnected this signal. When I try to connect I get a wi lan failed message. How do I get this resolved, I work from home sometimes and this is really bad for bussiness.

Thank you and look forward to your solution.