Connect to Router but not to Internet
 

We have a home computer in the basement hardwired to the router. We have a second home computer on an upper floor which I was able to connect wirelesssly through the basment router - all with no problems. The Computers were running under XP and router and wireless card are Linksys. I upgraded (?) the upstairs computer to Vista and immediately could not get a wireless connection even though I had downloaded the Vista driver. If I connect the upstairs computer by Ethernet cable to the router then I can connect to the Internet. But I cannot connect by wireless. I have spent HOURS with Linksys Tech Support and they have talked me through everything imaginable. What I cannot understand is how I can hardwire to the router and it works but I cannot wireless connect. The upstairs computer tells me I am connected to the router but cannot get from the router to the internet. PLEASE, any ideas?