I got this last Friday. Turned my laptop on - everything seemed to be normal. Entered my account password - and after the blue "Welcome" screen, at the moment when the desktop should appear, all I got was a black screen with the mouse cursor.
I tried all accounts, safe mode, quite a few reboots.
Tried F8 (recovery utility).
Boot repair didn't find anything. Memory check was ok. "Last known good configuration" didn't help. System restore point didn't help.
In the end, I managed to copy all of my files to an external HD via the command prompt using a nice tool called "robocopy" (see Wikipedia or google for it). If you use robocopy, READ THE INSTRUCTIONS FIRST or you'll end up with a big mess in the destination directory, or subfolders in the directory which you are copying will not get copied. This is the syntax I used, for example:
robocopy C:\Users\Daniel\Documents G:\a\Documents1 /COPYALL /E
Note that this is only going to work if you previously installed an external HD on your system. If you didn't, bad luck. I tried it at work (the problem occurred at work) with a colleague's external HD.
Using the "diskpart" utility, with the "list disk" command I could see it, but with "list volume" I couldn't. Using my own external HD at home, that one did appear with "list volume".
After backing up all of my files, I did a full system recovery. Unfortunately, on Toshiba laptops, you lose all content on the main partition (C
of your HD. On my newest laptop, the secondary partition's data does get spared; on my older (8 months) laptop, it gets erased also.
I suspect the cause to be some kind of virus (though it's weird that Avira didn't catch it; Avira tends to be pretty good). I hadn't installed any new software (or hardware) recently. So really, I have no idea what caused this...