I’ve installed ZBrush 3.5 but when I try to launch, I get the hourglass and a window button in the taskbar, but nothing else.
I read the top thread but it isn’t clear what I do for this problem?
I’ve run vcredist, and I’ve disabled my antivirus program.
Thanx.
Alt-Tab allowed me to see an error message I wasn’t seeing. It was telling me I don’t have enough disk space, which I do.
Anyway, once I OK’d the message, I was able to continue!
All OK now! 
Try running it as Administrator. In Vista this is the only way i can start Z.
I has the same problem (Vista64). As N8 said, run as administrator or open up properties of of the Zbrush.exe file and check the “Run as administrator” box.
I’ve created a ticket for the instructions to be updated.
-K