27mm
I'm no major expert on Windows, but this happened recently to a friend of mine, whom I help out with things computing/network-related from time to time. After some consultation with more knowledgeable WinFolk, we agreed the best thing to do for her was a system reinstall, as this is a fairly 'significant 'failure.
It worked well for us. Good luck with it and maybe someone might have better advice than me..
Jx