Welcome to the forum!
Regarding Moini's suggestion re malware, you might want to consider running your anti virus scanner, just to be sure.
After you restarted and reinstalled different versions, were you always using that same PDF for testing? I'd be interested whether the problem is happening in new blank docs.
When you say you were "cutting pictures from a PDF", do you mean you were cutting whole images out of the PDF and pasting somewhere else (or just deleting)? Were they raster images?
If it's a very large PDF with many raster images, and you always were using this particular PDF file for testing, it could be you just hit a typical performance issue with Inkscape. Raster images can rack up the MB really fast, and if for example, you had selected 5 images to cut or delete, or if for example, you accidentally moved them while selected -- that could lock up Inkscape.
But, if by "cutting pictures from a PDF" you mean you were using the Pen tool to draw paths, to cut them out - that's a different story, and unless there are hundreds of nodes, not likely to cause performance problem.
If none of that fits, and if you're still stuck after everything Moini suggested, I would suggest contacting developers. You could use the User mailing list
https://inkscape.org/en/community/mailing-lists/. Or you could probably find someone on the development IRC channel to help:
https://inkscape.org/en/community/discussion/Let us know what happens. I'll be interested to follow this.
