Had an issue today where my laptop refused to connect to the WiFi (despite repeatedly entering the correct password), while my Android phone had no problem. In fact, today the issue happened with 2 separate Windows 7 laptops (had to go to jury duty and took both my work laptop and personal one- neither would connect).
I had the same issue at PubCon in Las Vegas: our iPods and Android phone/tablet had no problems connecting to the hotel's WiFi, but absolutely could not connect my Win7 laptop nor my wife's Vista laptop.
No problem with the home WiFi for any of our devices. And I don't remember any issues with other public WiFi (Starbucks, etc.).
It connects to some WiFi spots but not others? It could be that you aren't able to handle the encryption key of the router if that's the case. Or it could be a number of other factors from hardware to software issues.