NO DHCPOFFERS received

I use ASUS 167G wireless USB lan card and Fedora Core 4
2.6.11-1.1369_FC4.

I've installed RT2570 driver and tried this description from <
http://www.stud.ntnu.no/~gronslet/bl...inux/#more-203
>
First time, it worked okay, but after reboot linux, my monitor is
vomitting follow messages if I run 'dhclient rausb0'

DICHDISCOVER on rausb0 to 255.255.255.255 port 67 interval 5
DICHDISCOVER on rausb0 to 255.255.255.255 port 67 interval 13
DICHDISCOVER on rausb0 to 255.255.255.255 port 67 interval 13
DICHDISCOVER on rausb0 to 255.255.255.255 port 67 interval 8
DICHDISCOVER on rausb0 to 255.255.255.255 port 67 interval 15
DICHDISCOVER on rausb0 to 255.255.255.255 port 67 interval 7
No DHCPOFFERS received.
No working leases in persistent database - sleeping.

my another commands are...

# iwconfig rausb0 mode Managed key restricted 135236361
# ifconfig rausb0 up
# dhclient rausb0

I installed FedoraCore 4 several times...and waste too much time.
Please help me~