I have a 4-year-old Sony VAIO Model number VGN-CS390JDV, Windows Vista 64 bit operating system, and two weeks ago, it randomly went to sleep even though I was using it (moving the mouse, typing, etc.) a minute before it happened. I was able to wake it up normally, by pressing a key on the keyboard, and it started back up as if it had gone to sleep (not in use for 25+ minutes). A couple days ago, the same thing happened again. This time I was even typing when it went to sleep.
The power plan my laptop is on is VAIO Optimized, with the display set to turn off after 15 minutes not in use and going to sleep after 25 minutes not in use. Both times it occurred I was just browsing the internet, checking email and chatting using google chat. My laptop also wasn't overheating both times.
Is there an explanation for why this could be happening? Thank you for any answers and help you can provide!