Notebook/Computer randomly shutting down

Notebook may shut down if its temprature is high. To resolve this issue, we need to isolate it first. I recommend to check, is the notebook shutting down when you are using any perticular application or is it shutting down when you surf the internet? If yes, then unistall the perticular software. Here are some steps to resolve this issue, if the notebook sutting down randomnly or if it not when you use any perticular software.

For Windows XP operating system.

Step 1: Disable Automatic Restart.

Right-click My Computer and click Properties
Click the Advanced tab.
Under "Startup & Recovery" options, click Settings.
Deselect the "Automatically Restart" option under System Failure"
Click OK and then click OK again.
Step 2: Download and install latest BIOS update for your notebook.

CAUTION: Installing a BIOS that is not designed for the processor in your computer, or interrupting the flash installation process may cause the computer to stop working

Step 3: Uninstall Power Management.

Click Start, select Control Panel, and then choose Performance and Maintenance.
Click the System icon to open the System properties window.
Select the Hardware tab and click Device Manager.
Click the plus (+) sign next to System Devices.
Right-click the ACPI Fixed Features button and select Uninstall.
Restart the system.
On restarting the system, Windows will automatically detect and install Power Management on the computer.

Step 4: Scan the notebook for Virus on your notebook. Use any good anti-virus program.

If issue persists then please reinstall the operating system.

The issue could be an hardware or with the motherboard of the notebook. But I recommend to perform above steps before arranging the repair service for your notebook.