Today, my iPhone was gone, so I put it into recovery mode and restore with jailbroken image. Right after restoration, I upgraded cydia and install Blacksn0w. After installation of Blacksn0w, iPhone was searching signals. But, it never got signal. So, I reboot but tt fell into infinite loop of restarting. I tried restore and install a couple of times, but I failed. So, I gave up unlock now.
It's interesting, since I installed blacksn0w before and there was no problem! At that time, I installed blacksn0w through SSH.
Maybe, blacksn0w cydia installation could have a problem or could it have any dependencies?