ports open on windows 2000

hi i have a pc(pc1) that i can’t connect to remotely, like any shares etc. i used to be able to but not anymore. I can ping it and when i go to the machine i can map drives to other computers, but nobody can map to the pc1, even though there is shares. so i am wondering if there is a firewall installed, the user says she doesn’t know, how can i see what ports are open on the pc?

thanks