I had a similar problem a year ago (different site).
Finally tracked it down to my router hardware. I could connect with no router, but not with router in the circuit - all else remaining the same.
 
Bought a newer model of the same router (Linksys - burning new firmware didn't fix it) and that fixed it.

So, when all the obvious stuff doesn't fix it, try connecting without a router.

BTW, I've been putting down Norton Anti-virus for years (I use AVG), but I hear their brand new AV is a total rebuild and (surprise) quite good.