I just did the following steps:
Everything works fine include Magento connect, but when I try to access the admin panel, it just shows me a blank white page with 500 internal error.
But as there is nothing in var/log and var/report, how can I find out what's the problem?
*I've already changed the permission and created the empty folder.
*I'm using Magento 1.9.2.4.
Ok. I've tried to fix it in last two days, but after post this question I found the reason accidentally.
It's a shame that I don't know why there're two adminhtml folders under design folder as following.
After I downloaded the project from server to my windows(That is the key point). It automatically left the capital one and deleted the correct adminhtml folder. Of course there was only app/design/Adminhtml in my git repository so error occurred.