ubuntu 12.04 pxe boot fail with message "IP-Config: no response after *** secs - give up"

ubuntu 12.04 pxe boot fail with message "IP-Config: no response after ***
secs - give up"

I followed the DisklessUbuntuHowto and set up my pxe boot service. When
configure the dhcp server in /etc/dhcp/dhcpd.conf, I tried to use static
ip address as follows, in which "00:22:15:F8:D9:1A" is the mac address of
the first network card in sms04 (it has two).
allow booting;
allow bootp;
subnet 192.168.0.0 netmask 255.255.255.0 {
range 192.168.0.21 192.168.0.30;
option broadcast-address 192.168.0.255;
option routers 192.168.0.50;
option domain-name-servers 192.168.0.50;
filename "/pxelinux.0";
}
host sms04 {
hardware ethernet 00:22:15:F8:D9:1A;
fixed-address 192.168.0.25;
}
When I boot sms04 using the first network card, it can successfully get
the ip 192.168.0.25 (static ip) and then load vmlinuz and initrd.
img1 (sorry for my low reputation, i can't post image)
And then it failed with message "IP-Config: no response after * secs -
give up"
img2
Now, I try to pull out the cable in my first network card and plug in the
second, after a while, it successfully boot up with dynamic ip address
192.168.0.21!
However, the dynamic ip address is unwanted. I try every method to boot
from static ip, by failed.
I will appreciate any reply.