My first suggestion would be to check the version of Firmware on the Linksys. We had similar issues with older versions of Linksys Firmware in the 1.35 & 1.37 version range. In our case, the client was able to connect, but not transfer any data through the Linksys. Things like email etc wouldn't come up. Give 1.42 or later a try, and see if that helps.
I suspect from your message you have tried this, but you could try using the udp port, as your ISP (or one along the way) may block the TCP packets.
If you have the concentrator behind a firewall, you may need to open up some TCP ports to permit this traffic to pass, there is info on which ports to open on the TAC website.
You may also want to verify that the pc and Linksys are getting correct IP addresses, you didn't say if the machine could get to other things on the Internet. If not, check from the dos prompt ipconfig /all and verify that you are getting an ip address from the linksys, and check the linksys to make sure it's getting an ip from the DSL provider. If addresses are missing, power off the DSL modem, the linksys & the pc, and start powering up things closest to the Internet first, let each one fully boot up, and go on to the next device, until they are all up and running. Then verify that they all have the proper addresses.
Hope this helps, we see all these on a regular basis. - Bruce
