System Shutdown... NT AUTHORITY\SYSTEM
This is a default setting option in Windows Xp (that I know of) and easy to fix. Upgrades are always suggested and you can do this by using the "Windows Update" icon in the Start menu.
To fix the problem, you simply need to clear some settings:
1. On the Desktop, right click "My Computer" then select "Properties": My Computer->Properties. This opens up the "System Properties" dialog.
2. Select the "Advanced" Tab.
3. Under "Startup and Recovery", click the "Settings" button.
4. At the bottom, in the "System failure" section, see which boxes are checked. Windows XP checks them all by default.
5. Uncheck "Automactically restart". This is likely your cause if you are getting automactic shutdowns. AS an alternative toward optimizing this method further you can, at your own discretion, also do the following:
i. Uncheck "Write an event to the system log"
ii. Check "Send an administrative alert" (which should do more than display the sudden error rather than shutdown).
iii. Uncheck "Automactically restart"
iv. In the "Write Debugging information" section's combo box, select "(none)". Note that this will disable the rest under "Write Debuggin information".
6. Your finished and click "Ok" to close the sub dialog and then "Ok" again in the "System Properites" dialog.
That should do it. Some of the suggestions of upgrading are propally best, but I think these only handle security issues regarding other areas though they are worth the 2-5 hour downloads in 56k modems for the added security. However, I find that some of the updates are not even for my type of setup (due to unused configuration detection?) or I do not use the services.
For more information on Tweaking, I suggest looking at "http://www.tweakxp.com" if you are a Windows XP user.
Good luck.