On my PC the scanning stopped at 48%. I waited 10 minutes and was still at 48%. I quit the software, but my PC still sounded like it is being defragmenting. I tried to restart it via Windows (XP), but no luck. I had to press the reset button on my PC.
After using Defraggler for 2 days without any problems, it gave me a black screen Too bad, because it's a great little program. Now I have to use Auslogics again
I also thought, that it frozed a few times, so I hit reset, but it did not, it just needs time to optimize files on the HDD, because it does not only defragment them, it also puts them in a line from the beginning of HDD. So it is not the fastest one, but it does better job than Auslogics, which I used for a few months and is obviously weaker, so just give it a time, get a coffee and let it finish, you will surprised, how fast it is everything gona be afterwards.
I have experienced 'freezing' issues when defragging very large files (4GB+). My computer was essentially frozen until Defraggler finished defragging the file in question, even though i was defragging a file on a completely different hard-drive from my OS (NOT a partition).
Maybe the Piriform guys will look into some priority tweaks in the next release.
I'm having the same issue. When I run a full disk defrag it hangs at 94%. When I close Defraggler the process keeps running and it's using 50% of my processor. I can't stop the process and can't shut down without forcing a shutdown by holding down the power button. I'm running Vista.