Vista - Virus, firewall, or registry problem blocking internet for windows update

Hello and thanks in advance for your assistance.

My problem is this: Windows update is unable to download anything from the update servers. It alternates between an error that says it can't connect to the internet, and an error that says it's already installing other updates, but it is not. Additionally, AIM and Yahoo messenger will not connect. I believe these are related somehow. I use firefox as my main web browser. Both firefox and IE are working smoothly, with no interuptions in my connection to the web.

I have had a number of recent changes to my system setup that could potentially be to blame. I will list them below.

-Norton AV subscription ended and was not renewed, causing me to pick up a number of viruses and rootkits.

-Used HijackThis and Malwarebytes to clean computer up, eliminating some registry keys.

-Kept getting the viruses and rootkits back.

-Subscribed to Norton 360, which seemed to clear up all virus problems.

-Purchased a new router.

I'm running windows vista home premium 32 bit. I have a 2.2 GHz dual core, HP. 500 gig HD, 2 gigs RAM, Gforce Video card with 512 onboard memory, on a wireless N router/USB adapter. My PC came with vista pre-installed, so I do not own a disk, only a restore partition.

Let me know if you need anything else, and again, thanks in advance.