quicksand wrote:Crashes can be caused by bad drivers or some of the more system intensive programs (some graphics stuff like Maya, some versions of Flash etc etc). It hasn't always been like this, so there is a time when this became noticeable,..try and recall what time that was. You might find that this has been triggered soon after by something you installed, to eliminate the problem you just need to isolate and remove that software
This explanation by
quicksand is correct!
On the other hand, if you have not installed knowingly or unknowingly any software lately, this could be a sign of some hardware failure. You probably need to let the machine to cool if it has been overheating. In addition, check that your working surface allows for proper heat conduction from the machine.
In the case that you are totally unlucky, then some piece of hardware has given up, including the motherboard. Easy way to check could be by replacing the memory unit and hard-disk.