* Weak Memory Module
* Bad Motherboard
* Bad Power Supply
* Incompatible Software or Drivers
Note: It is important to remember that when you have difficult troubleshooting problems such as this, you need to start with the steps that are the most simple and that don't cost any money. This could save you time and money!
Overheating:
Accumulating dust in a computers case can cause a great deal of problems with computer systems components. Dust acts as insulation and will keep the case and all of its components hot. I recommend a computer case be cleaned at least every 6 months.
Bad Motherboard:
Malfunctioning capacitors on a Motherboard can create a wide range of issues. It is even possible for capacitors to fail due to a bad Power Source. A leaking capacitor is a very easy visual check. Open your case and take a look at the Motherboard. If you see a leaking capacitor (see the image below), then replacement of the Motherboard is necessary. Be sure to check if your system is still under warranty before spending your money.
Swollen/Leaking Capacitor
Incompatible Software or Drivers:
If you have installed a new application lately or updated a driver, this may be the cause of your system reboots. Try uninstalling the program or use system restore to roll back your system to a known good configuration. Also, be sure that all of your Windows Updates are installed.