I have a VAIO laptop: VPCF13CGX, with a 64-bit Windows 7 Professional installed. It works fine, but sometimes it suddenly goes to sleep! I must press a key afterward to wake it up (of course), and after it wakes up my Wireless and USB devices do not work! Therefore, I have to restart it.
After searching Windows event logs (for Event ID 42; which is Sleep event) I found the following:
The system is entering sleep. Sleep Reason: Button or Lid
But I neither pressed the power button nor closed the lid. Therefore, something is simulating this behavior on my system.
PS: (I have updated the graphics driver to the latest version, so this can't be the reason).