What firewall are you using? You shouldn't turn it off, just set it to allow limewire access to the internet.
Firewall configuration instructions (click on link).
Who is your ISP? They may be blocking p2p programs.
If your connected through a modem/router you will need to configure it also. Most contain a nat firewall. You'll have to look it up and configure it accordingly:
Connection problems? Check here first!.
If your firewalled you probably won't be able to become an ultrapeer.
You can't make yourself become an UP but you can increase your chances by configuring you setup correctly and leaving limewire running for extended periods. Then if LW needs one and you have enough bandwidth to spare you might become an UP
. I'm not ure what the advantages are. I think someone said you could get better search results(not sure), but the advantage is minimal.