Hello Vesna,
Unfortunately, I don't think there is much to do to recover photos that you can't open with usual tools. Copying them to an external hardrive won't help.
But, before doing anything else, you could try opening the problematic photos with another program that you can download freely from the internet. It is called FastStone Image Viewer and can be downloaded from here: 
https://www.faststonesoft.net/DN/FSViewer75.zip .
Just download the file to your computer, unzip it to a separate folder and run the file named FSViewer.exe.
It is the portable version of the image viewer, which means that it doesn't require installation.
After opening the FastStone Image Viewer, just go to a few of the pictures you can't open and try opening them. If the operation is successful, then it means that your pictures are OK and probably something went wrong on your computer system that prevents opening certain jpeg files.
After that, you can try backing up your photos on an external hardrive.
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