1. How many times would you be able to know who logged in or who used ur computer in your absence?NOt much most of the times!!!An easy to find out the details is a one liner solution......
2. So,here is the trick for that ..Simply type as given below in the RUN bar ie
Start - Run - TYPE eventvwr.msc
3. All details of login will be in front of your eyes.SIMPLE!!!!!!!