well, first, you would check your own PC's firewall settings - ask whoever installed Linux on the PC to check that.
Or, you would check to see if you're behind a router (that is, if you have a lot of comps connected to a router that's connected to your modem...) and check to see if the router is blocking those requests (routers can usually be accessed at http://192.168.0.1 or http://192.168.1.1 depending on the brand)
Hope this helps.