12.10 unexpected shutdown-Collection of common programming errors

A week ago I upgraded my system from 12.04 to 12.10 and now I am experiencing unexpected shutdowns. I did not have this problem at 12.04. This happened twice in a week and it takes a while to load my user settings when I re-open the system after unexpected shutdown.

Do you have an idea what can be the reason for this situation? Is there a log-file which I can see the reason of the shutdown like overheating or xx application crash etc?

Regards

note: At the second time, I was only watching a video on youtube by chromium, no other programs were running. (only everypad and dropbox were running in the background) At the first time I was coding MATLAB and again chromium was open and listening to music on youtube. I do not know if something related to flash player can be a clue?