For a while I have had no problems with my Asus laptop running Windows 7. It is a decent computer and I need it to run almost 24/7. I restart it every few days but it does continuously run. However, recently my computer has randomly been going into sleep mode. This from the best of my knowledge, has been after I have not been using the computer for a while.
Before people suggest the more obvious solutions, I have checked all power settings for my laptop. They all say never/always on.
Oftentimes the cause of this sort of random hibernation/shutdown is overheating. Most computers are set to hibernate if the internal temperature reaches a certain level. A friend of mine has an Asus laptop, and it tends to run hot. Speedfan is a very popular piece of software which can be used to check the temperature being reported by your computer's internal sensors. You should be able to find a datasheet for your CPU, which will tell you the heat tolerances, and whether it is in fact the heat that is causing it to hibernate.