Two things come to mind. First is to make sure you have a tftp server installed, and second is to make sure the a line something like this:
next-server 192.168.1.4;
is at the top of dhcpd.conf. (Replace 192.168.1.4 with the IP address of your tftp server.) Here's a how-to on diskless booting. Although it's not for Fedora, it may be helpful:
Diskless Debian How-To