I recently found this at the Microsoft Support site. It's a "feature" that let users trigger a crash dump for testing purposes.
Step 1: Step 1: Editing the Registry
The first thing we'll do is to edit the registry.
To do this in Windows Vista:
In the Start Search box, type regedit. Hit enter. (If you are prompted for an admin password or confirmation, type the password or provide confirmation.)
To do this in Windows XP:
Go to Run. Type regedit and hit Enter.
Now for the editing:
1. Go to HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\kbdhid\Parameters if using a USB keyboard or HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\i8042prt\Parameters if using a PS/2 keyboard.
2. Add a new DWORD key called CrashOnCtrlScroll and give it a value of 1.
3. Reboot the computer.
Step 2: Step 2: Triggering the BSoD
After we log back in, we can now trigger the Blue Screen of Death. Just hold Ctrl and hit Scroll Lock twice.