If it sent out DHCPDISCOVER and never gets a DHCPOFFER then either it timed out (stopped waiting for an OFFER) or the DHCP server is broken/not-working/not-serving. IF you want to know a bit more about how DHCP works, then http://www.softwaretipsandtricks.com...53&postcount=5 is a great link.

As for you situation, try stopping & restarting networking (does not require a reboot). As root user:
/etc/init.d/networking stop
then
/etc/init.d/networking start