Failed to use wireless net work in Mac.

After hair cut, I got to Macdonald near by. I had an aim to get there to enjoy internet with wireless network which is provided by Yahoo BB as well as had a lunch. Many Macdonald shops install the system . So I made a contract with Yahoo to use the system and I'd already got some passwords. I ordered small size ice-coffee(120-yen), got it ,and went up to 3rd floor. Every seat at 2nd floor was filled with customer.
I was happy to find spesific seat for computer user there.(I can also use electricity freely threre anbelievable.) I opened my bag and took out my computer and tried to use it
But I coudn't use wireless network at all. I was dissapointed.Although I asked a staff how I could deal with it, the staff said she didn't know about it. So I gave up.
Actually it was my second time to try it. Last time my comuter found signal of wirelessnetwork.But I couldn't check in the system. One time I asked a stuff of Yahoo BB information center. He replied he could't do enything unless he could confirm the fenomina in actural situation .I remenber my wife told me. "What't the point of making a contract of "Mobile point",if you don't have many oppotunities."
I have to pay 300-yen per month to keep the contract.I don't know I can use the system in the

future.