Know how to fix a wireless connection identification problem?

I have this odd problem with my vista laptop, when I connect to my wireless network , it marks it as an unidentified network , and will not connect to the internet. My sister’s laptop connects perfectly fine with the exact same network, and the home pc that I’m on now, so the problem must be with my computer itself, I have run multiple system diagnostics , nothing comes up. The only solution my computer can come up with is to visit the microsoft website and download a software fix into the computer , which might work if the problem wasn’t I could access any websites.

So mainly, how can I get my computer to identify my network and connect to the internet?