Do i have a firewall? I can't use Limewire. I use win 2000?

I used limewire last night, and I tired to use it today. It won't connect. It says i'm behind a firewall. (I don't know if it said that before when it worked, but I'm going on the umption that that's the problem since I've never added a firewall to my computer. not to my knowledge anyway) I went to an online firewall tester, and it said my firewall was working fine. I didn't know i had one.... I use a router, but i haven't messed with it, so i don't see how that could be the problem. Any suggestions on how to make Limewire work again?