HI all,
First, I have flashed my white Beaglebone to lastest firmware, then I was upgrading my opkg using "opkg upgrade" command in my beaglebone.
After a few minutes, my beaglebone freeze. It is keep restarting now. I can not boot up, it just keep restart if even it I replug it.
Has anyone seen this problem?
many many many thanks
Welcome to the forum, yizhan wang. 
Yes, that problem has been seen quite frequently before --- it was often mentioned in the Beagleboard Google group and in the IRC logs. I haven't been looking in either place in recent months, but because the problem was known and was in the process of being fixed, I would have hoped that it had gone away by now.
Apparently not. 
For what it's worth, the non-masochists leave Angstrom behind just as soon as they can, and switch to ... well, to anything, as long as it's not Angstrom. The name begins with "Angst" for a reason. Many things are broken on it, they don't get fixed (as you are experiencing) because nobody seems to be charged with maintenance, huge numbers of packages are missing, and Angstrom support ranges from minimal to outright belligerent.
So while I sympathize with your predicament, the strategic way of getting out of it forever is to buy a 4GB micro-SD card and write some standard non-Angstrom image to it --- Debian Wheezy for ARM is a favourite of many.
I know this doesn't help in a direct way, but I ceased wanting to fight that unhelpful distro many months ago. No other Linux system I've used (and that's a large number) has ever been so poorly supported and a stumbling block to getting work done, and as you experienced, simply broken.
