I found this fascinating quote today:
There may be a simple explanation. With most modern computers, the system comes with built in circuitry to monitor the state of the computer. One of the checks built into your system include testing the power supply levels. The power supply is not a component most people expect to fail. Most are concerned that their disk drives will be the major cause of failures, but in fact power supply problems are relatively common. The power supply will communicate to the mother board with a power good signal if the power output is within specification. If this power good signal is not present, the computer will simply not start up. This seems simple enough, however things do not always fit into the good or not good categories. Where you have a power supply that is failing, its outputs can fluctuate. The computer may then boot up correctly, but a little later when the power supply falls out of range the computer will detect this and activate the reset logic. The reset logic shuts the machine down, thus relieving the load on the power supply, which can then support a re-boot. It is the same as if you pushed the reset button yourself, but it appears to you as a random re-boot.The Symptom – Power Reboots For No Reason, Nov 2008
You should read the whole article.




