I think that everybody who works with Fedora Core noticed that software installation utility YUM hangs up sometimes. I happens for me after killing yum process during it downloads package or etc. Next time I start yum, it hangs up. Here are two commands to avoid this:
killall -9 yum #to kill stopped yum
rm /var/lib/rpm/__db.* #to prevent hanging up
After it’s done, yum will start normally.