I am using Ubuntu 12.10. I always keep my computer updated. Now, for some strange reason, whenever I start watching any movie, the computer restarts randomly. I tried watching with VLC, totem and mplayer. Result is the same. Can anybody tell me what can be possibly wrong? And there must be some log files including informations during the restarts. Can someone tell me where I can find those logs? Thanks in advance.
It could very well be a graphic card bug. I would make sure your graphics drivers are up to date, and if so, file a launchpad bug. So much of movie playback is hardware accelerated now, that subtle bugs can creep in.
You will probably also want to clarify in your question what you mean by restart. Does the full system reboot, or just the user interface crash and you go back to the login screen?
The following guides have been helpful to me when debugging system crashes. To be clear, I think you have a genuine bug of some kind, and I think you should file it upstream. I know that doesn't help you watch movies. :(
I don't see anything obvious in your log files. A true kernel crash will not show up in log files usually, and if find that is what you have, you will need to enable the following to make forward progress:
Sorry that you are having this trouble. :(