The thing to do is first manage your startup menu to disable everything that you do not need to run in the background. Things like Realplayer, Adobe viewer, Microsoft Office or any of its components.
What you do want running are system aps and anti-malware aps like your anti-virus program, anti-spyware and anti-malware aps,
Use Startup Inspector to manage your start-up menu:
Startup Inspector (manages startup menu – helps you identify aps in the startup menu so you can disable unnecessary programs from running in the background when they are not needed)
Startup Monitor (a small freeware ap available on the same page to notify you and require your permission for any program to add itself to your startup menu)http://www.windowsstartup.com/download.php
After you do that, read the following and do as it instructs:
How to handle spontaneous reboots in Windows XP:
When a critical error occurrs in Windows XP, the system will reboot automatically by default. After the reboot, Windows will then usually show a dialogue with the explanation that the system has recovered from a critical error and will offer to submit this error to Microsoft.
Most of the time these spontaneous reboots are rather unique and are not an immediate cause for alert. However, if the situation is recurring, there is probably something wrong in the system configuration. To get a good idea of what is wrong, it is best to disable the option to automatically restart the system after a failure, but to let it show the error message instead.
To do so, please perform the following steps:
1.Right-click My Computer.
3.In the System Properties, select the tab Advanced.
4 In the box called Startup and Recovery, click Settings.
5 A new window will open:
1.Uncheck the box "Automatically restart" in the group System Failure
2.Confirm the changes in both Windows by clicking OK.
Whenever a critical system failure occurs now, you will see a blue screen with a cryptic description of the error. However, the content of this message might help in finding the appropriate solution to the problem.
Note: Most of the critical errors are due to faulty driver installations or incorrect BIOS settings. Especially in case of misbehaving drivers, the blue screens often list the filename of the driver that caused the crash.
Copy the exact (and complete) message you see in the blue screen and post it here so we can diagnose the cause and help you repair the problem that's causing it.