To fix an error,you should first know the error and then find out what causes this error.
System errors in Windows occur all the time(the pretty blue screens of death).The default settings Vista (or even XP) is configured with is to simply restart on own.
While this is a common way of troubleshooting errors,not all system errors can be fixed by a simple reboot.It is important to get details of errors when they happen so they can be analyzed.
To prevent Vista from auto-rebooting whenever a system error happens,navigate to Start > Settings > Control Panel > System > Advanced Settings.
Select the Startup and Recovery tab and uncheck the automatically restart option.Click OK to save the changes.
Doing this will ensure that Vista in event of a critical system error will come to a halt which in turn helps in seeing the error (error codes/description in case of blue screen).
Hope this has been an informative post.