I've had this problem over a year, reported about it here, and gleefully try every new version of XTU hoping that it incorporates a fix, but alas, 12 months later, there is still no resolution.
As long as XTU is installed, the DX79SI will transition to sleep, however the fans will keep spinning, and the machine turns into a zombie. The only way to wake it up is to kill mains power and let it cold boot.
I know for a fact other people are seeing this behaviour, and its easily reproduced. Install Windows, install drivers, install XTU. Wait for system to sleep. BAM! Fail!
What can I do? Besides whinge on this community page?!?
Jezzarino, I would need to try to replicate this behavior, we haven't heard anything about this.
Are you running the latest BIOS version and drivers?
Which processor are you using?
Latest BIOS, latest drivers, latest XTU, happens under Windows 7 64bit, Windows 8 64bit and Windows 8.1 64 RTM
CPU is a 3930K
Set the machine to sleep after x amount of minutes. Machine sleeps. Wake it up, then wait again for it to go to sleep, and it will fail...