who used ur pc in ur absence

First you should go
start > run >eventvwr.msc

Events are stored in three log files: Application, Security, and System. These logs can be reviewed and archived.
For our purposes we want the System log. Click on "System" in the left-hand column for a list of events. Look for a date and time when you weren't home and your computer should have been off.

Double click on the eg: info and it will show you the detail.

You can also use this log to see how long someone was on the computer. Just look at the time the computer was turned on and off for that day.

Hope you all will like it.