|If your CPU heat sink/fan and even case fan and vents are clogged with sufficient dust you may not be able to remove enough heat from the CPU to keep it from overheating. I know it sounds like you should have more than a few seconds, but if the CPU fan is not turning and the fins are clogged enough the dust is acting as an insulator and allowing the heat to climb fast.|
If your CPU heat sing is no longer locked down properly (from being knocked around or being messed with) you will need to remove the heat sink, clean off the thermal paste, and add the proper amount of thermal compound when you reinstall the heat sink. See:
You could also have a memory issue. Use Memtest86 to test.
You have to be a little bit crazy to keep you from going insane.