can’t get an dynamic ip address

hi there
i am using a wireless conection to connect to the internet , the wireless isp enabled the dhcp server , and it use an mac filter to make sure of ppl who connect to the network , when i am connect to the network i don’t get an ip adress i just conect to the netwrok , my mac is valid i am at the network .but i can’t recieve packets , i have the dhcp ip the dns the gatway and ip adress , other users get an ip from the netwrok it just my problim i am using windows xp profisional