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after that I downgared it back to 2.3.6, and I could not turm it on back again
When turn it on, the wifi shown searching later 10-20 seconds it turn off by itselve.
When you upgraded, and then downgraded, did you do a factory reset?
I would download and install Kies from the Samsung website and backup all the data you need. And try a factory reset.
This seems to be a pretty common problem with the upgrade from GB to ICS. It sucks to lose all of your apps, but a functioning phone is better than no phone.
Any apps you downloaded from Google Play should automatically re-install when you first sign in to what used to be called the Market, so I'm not really sure how you'd lose them. Same goes for Amazon App Store.
GSM Galaxy Note 3 (Black) - Straight Stock
GSM Galaxy Note 2 (Titanium) - Rooted running Jedi X20 Rom
GSM Galaxy Nexus (Black) - Straight Stock
GSM Samsung Galaxy S3 (Red) - Rooted running Deadly Venom v8.0.1 Rom
I can't say for sure as you have done all the things I would have done. If the WiFi is still acting up, is there any way you can bring it back to your carrier or send it back to Samsung?
I have done a little reading on the issue, and it seems with the upgrade from GB to ICS screwed up a lot of things, namely WiFi as far as I have read.
[Solved] WI-FI Connectivity Issues in Samsung Galaxy SII – s2 – I9100 « Chaladi's Blog
I would try reading this page, and see if any of the items helps out your WiFi issue. Let me know how it goes.