Unable to connect to certain sites

The story so far-
About 5 days ago, I started having difficulty connecting to certain websites- my email, online banking, smugmug (photo sharing), CNN, Windows update, etc. The error message comes back saying 'Firefox couldn't establish a connection with the website...'
Note: I can connect to the Yahoo home page, and can get to the login screen, but after entering my login/password, the connection times out. Subsequent connections to the Yahoo page show my mail preview, but again, times out when I try to access my in-box.
Sites that seem to be more 'open', like forums, google, etc, I don't have any problems with.
I ran a complete system scan with Norton 360, Spybot and Malwarebytes, and only turned up a few cookies.
Since the scan didn't turn up anything, I did a complete re-install of windows XP, including a full format of the partition that windows was installed on. (This includes re-downloading new browser software- nothing was 'restored' from other drives.)
The problem is still there.
What's interesting is that I have two computers in my house- one wired to the gateway, one (mine) connected wirelessly. I don't have any problems with the wired computer (I can connect to the above websites), which suggests that the issue is something to do with either a) my computer or b) my wireless link.
I've done the speednet speed test, and am getting 3megabits/second down and .94 megabits/sec up, with latency of about .27.

I'm reasonably computer savvy as far as the basics go, but not very familiar with more detailed stuff.

Oh yes- I did spend 30+ minutes on the phone yesterday with my ISP (AT&T) with no resolution. They're supposed to be calling me back today to continue trying to find a solution.

Hope someone can help,
G

 

Hi gweaver,

This is Mike from the Norton Authorized Support Team.

There are two features in Spybot that you need to disable, as they can cause a software conflict with Norton 360 which can contribute to connectivity problems. The features are the "Tea Timer" and "SD Helper" functions. You can disable both of these by entering Advanced Mode in Spybot and then entering the Settings section. After you disable these settings, restart your computer.

Next, make sure you have the latest version of Norton 360 installed, which is version "3.5.2.11 ". If your version does not match, manually run LiveUpdate and then restart your computer after the updates have been installed. You may need to repeat this step a few times until Norton 360 informs you that there are no more updates available.

If you still have problems connecting to certain sites, please follow the instructions in the document below.

Help with connectivity problems with Norton 360 3 installed


Thank you,
Mike