If I guessed right, you have this virus on your pen drive...
First of all, press Ctrl+Alt+Del and go to running processes to see if RavMon.exe is already running in your processes. If yes, end that process.
Next, right click on your pen drive icon and click "Explore"..
This is important... DONT CLICK on the pen drive icon... dont autoplay.... just right click and explore...
Now you can delete both autorun.inf and RavMon.exe