Hi Andrei,
I am Dave, I will help you with this.
Click your Start Button, then just type resmon.exe and press Enter
That will open the Resource Monitor utility
Select the CPU tab
Then close up the Processes and Services sections
In the search box on the 'Associated Handlers' section, type the exact path to the ISO you are having difficulty with.
That should then show what process(es) or application(s) is accessing the ISO.