Have you tried deleting the networks and then reconnecting to them?
Try setting yourself up with a static to see if it connects.
That will tell you if it is making a true connection.
From the properties of the Wireless connection scroll down to the TCP/IP Properties.
The majority of Linksys/Dlink/e.t.c routers are set to a class C subnet, i.e. 192.168.1.0/24
So, knowing this enter the following:
IP Address 192.168.1.100 (If you get an IP address conflict error change the last octet in the sequence i.e. 100 to 101, 102, e.t.c)
Subnet Mask: 255.255.255.0
Gateway: 192.168.1.1
Primary DNS: 192.168.1.1
If that still doesn't connect to any of the networks then you know you don't have a true connection and you need to do what Roshan suggested first which is removing the networks from the saved networks listing and trying to reconnect (Make sure to set IP information back to "Auto" after doing this so DHCP will assign you a new IP if it does indeed work)
If that doesn't do it, then they've either found you out and changed the WEP/WAP keys, Their router/access point is misconfigured, or there is something wrong on your end.
Oh, and for shits a giggles let's try rebuilding your Winsock.
Download and run the following:
http://www.snapfiles.com/get/winsockxpfix.htmlJust in case your shit is on the fritz, never hurts to run it either.
Let me know how it goes.