I've read all topics about white screen of death and I didn't find the solution of my problem.
The thing is that I have created a network of 265 blogs. I use the domain mapping plugin in order to have every single site working with different domain.
Unfortunately some time ago I started getting white screen of death when I try to enter /wp-admin/ in the main site and in each single blog. All sites are working properly, but there is no possibility to enter the admin page. I can't find the reason of this situation. It just started without my interference.
I've tried everything. Firstly I thought that someone hacked my network. I searched files for any changes, I reinstalled my WordPress and it didn't help.
Then I thought that one of my plugins could cause the problem, so I changed the name of my plugins directory. The result was the same - white screen.
I searched my datebase for any signs of hacking, but I couldn't find nothing.
I looked for phrases: iframe and noscript.
Do you have any ideas?