Backtrack 4 R1 won't connect to my wireless access point

Hello,

I tried to sort this out and it worked a few hours ago, then it happened again but this time I can't fix this problem.

Backtrack 4 R1 detects my adapter but when I try to start networking it comes up with this "DHCPDISCOVER on wlan0 to 255.255.255.255..." then at the end of that command it says "NO DHCPOFFERS received."

Then I try "/etc/init.d/wicd start" then "iwconfig wlan0 essid "ESSID HERE" key KEY" then "dhclient wlan0" then it says "DHCPDISCOVER on wlan0 to 255.255.255.255..." again.

I've tried everything to sort this out, I've tried "modprobe r8187" this just comes up with "FATAL: Module r8187 not found."

Any help would be appreicated

Thank you