I had this problem with linux mint. It freezes unexpectedly and everything stops working, with the power or reset button being the only solution.
This problem has happened during various uses. While using transmission, firefox. On firefox it always freezes whenever I put the videos in fullscreen on youtube. It has even frozen while the computer was on, doing nothing.
This may be a Linux Mint issue. Yesterday I bought a new motherboard, but this problem also occured when I had my old one.
The graphics card isn't the problem because that's new too. Same goes for the hard disk.
I was beginning to think that it might be a RAM problem, but the memtest thinks my RAM is working just fine.
The only thing that's left is the CPU or the Power Supply, and as long as I am aware of the CPU almost never has problems that freeze the computer. I am also using Windows XP SP2, and I never had any freezing problems or Blue Screens of Death, so that should be enough for me to think that the problem is not hardware-related...
Any ideas? I strongly believe that it is a Linux Mint bug...and a serious one. It has also happened to my new Dell laptop. The same thing