Thanks, UnFleshedOne.
OK i managed to solve the problem with your tips.
What I did:
1. remove battery and put it back after 20 seconds or so..
2. flash the bios...
3. go to bios, disable all power related setup. If you are using Intel i7 CPU (my case here),go to the CPU setup and disable the automatic speed adjustment function called turbo boost!!! this is the key issue!!
Then the problem should be solved. I asked my friends working in another motherboard in China. To be fair, the problem is not necessarily caused by Gigabyte. Gigabyte and another popular motherboard brand use ITE (
www.ite.com.tw, a Taiwanese chip maker) chip to monitor hardware status and temp. It also can adjust speed of your fans. However, i7 CPU's built-in adjustment doesn't seem to be working fine with ITE's chip. So if you enable i7's power management function ( Turbo Boost Technology) and use RAID, who requires ITE's chip to monitor status, you cannot shut down your PC properly.... there are los of similar problems for that brand as well. The solution is very simple, disable all power management related setup in BIOS. it can be solved although you won't be able to enjoy "turbo boos" from intel.