Bad theme can make your admin blank

I noticed some people are having problem to access their admin after upgrade(blank page in my case), so am I. I tried to deactive all plugins, chnage the config file and other things but no luck. Until I found a theme called googlechrome (ver 1.04) is the cause of the problem. I finally know that a problematic theme can cause trouble as well.

Now, my sites are working again after I remove that theme. If you got the same problem like me, test your theme one by one to see if there is any problem.