Sounds like your up2date is pointed to a bad repository, or one that is too slow or unresponsive. You can check /var/log/up2date and see what it's doing (or not doing). You can go to /etc/sysconfig/rhn/sources and change the path to another location so you can download from another source. You may also want to try running up2date-config and see what that does for you. You can visit
www.fedora.us and click on Mirrors to see a list of available repositories you can connect with and maybe choose one that is more responsive.