There was  movie on my hard disk which has mkv format and When I'm going to delete that mkv file, it is prompted with following error message.
" the action can't be completed because the file is open in windows explorer "

 

 and it doesn't allow me to delete it at all. I restarted my computer and try to delete it but same error no luck. Finally I have found a solution , it was very simple than I thought . This is what I have done

[1] open command promt

for windows 7 , click start and type cmd

[2] Change the directory where delete file is located

in my case, file is at Desktop and I used following command to change the directory
cd c:\Users\Admin\Desktop

Now try to delete file using command line , issue following command
del "file name"

but you will get an error message similar to following for sure :) don't worry !!
" The process cannot access the file because it is being used by another process. "

[3] Disable "explorer.exe"

open the task manager , select "Process" tab and select "explorer.exe" from the process list and click "End Process" button
Now every thing should be vanished except command promt and Task manager , don't be confused we will get back them all later :D

[4] Delete the mkv file

Now again issue del command , this time it should be executed and you will get no error messages.
ok , big step is done , now time to get back desktop and task bar

[5] bring back desktop and task bar

type explorer.exe on command prompt . how simple it is :))