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).
I would recommend to try the following steps:
Step 1: Update the BIOS - It is possible that your BIOS cause these problems. So have a look at your BIOS-Version and if there is a newer version available, than update it.
Step 2: Check your BIOS-Settings - When there is an option in your BIOS-settings which contains "wake on lan", disable it.
Step 3: Use an Ubuntu Live CD to check if windows is the problem - Maybe it isn't windows which causes the "error". So you can use an Ubuntu Live CD and watch a movie or something to check, if windows causes the error or if the pc itself goes to sleep because of an overheating or something like that.
It may be a magnetic band in your watch, Nike fuel device etc. The sensor will think that the computer lid is closed and will trigger the device to go into sleep mode.