I found this online somewhere but here it is:

Windows-XP has a "feature" (???) with which it is possible to manually crash a system by simply holding the right CTRL key and pressing the "Scroll Lock" key twice. This feature can be turned on by the following steps:

1. Start regedit. (If you are unfamiliar with regedit, please refer to this FAQ)
2. Navigate to:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Servic es\i8042prt\Parameters
3. Create a new DWORD value and name it CrashOnCtrlScroll
4. Right-click on this newly created value and click on Modify
5. Enter 1 in the Value data field and click on OK.
6. Close regedit and reboot your system.
7. Now you can blue screen (crash) your system by holding the right CTRL key and pressing "Scroll Lock" twice.

Note:

Your system may reboot or show a blue screen whenever this crash is initiated. If your system reboots after initiating the crash, and you want to see the blue screen, follow these steps:

1. Go to Control Panel > System
2. Click on the Advanced tab
3. Under Startup and Recovery, click the Settings button.
4. Under System failure, uncheck the option Automatically restart.