I have the same problem, for the past year or so. I have cleaned out the dust and the computer has plenty of space for air flow. There are no errors in any of the evnt logs and no warning. Just boom. It does seem like I can predict the shut down. The cooling fan shuts off after running for a while, then it shuts down. It think there is something in the bios that is incorrectly controlling the fans, I have done a lot of research and it seems that the problem is occuring with manyAcer all in ones and laptops.
My aspire shuts down by itself as well. It usually happens when I am on FB playing bejeweled blitz or using a program such as pandora. I'm thinking it has something to do with the graphix controller or something. Its very frustrating. I have checked my status and found that it has several events logged. Nothing serious but stil?!?! Anyone have any solutions????