Reliability Monitor is an advanced tool that measures hardware and software problems and other changes to your computer. It provides a stability index that ranges from 1 (the least stable) to 10 (the most stable). You can use the index to help evaluate the reliability of your computer. Any change you make to your computer or problem that occurs on your computer affects the stability index. This starts its journey with Windows Vista. In Windows XP, there is a tool under Control Panel -> Administration, called Performance monitor, this the equalent tool for Reliability Monitor.
To get this
Search for “reliability” from the Start menu, and run View reliability history.
In Windows 8, this tool lay under Settings.