I had a problem when I first d/l LimeWire I couldn't connect - no hosts, no search results - nothing - dead as a Dodo.
Then I tried my other ISP - unfortunately this one costs more.
BINGO - I was connected right away - well, within about 30 secs.
I rang my ISP - the one I couldn't connect with at first and they made some lame excuse about having problems and it would be fixed within 10 days. That was 2 months ago and still I can't connect through them - Maybe they're running scared.
I can't be bothered to ring them - I just use the one I can connect with.
This might not be the problem with yours, it could be something else - the only way to test this is to have 2 ISP's like I have.
But at least this post has taken it back to the top of the heap where you might get more help if my post is not the answer.
It's a bit like going to the docs - it takes them a little time to figure out what ails you.
Good Luck
Kath