Thanks, both of you.
Yesterday I read on some (German) forum that it might indeed be a software problem after all and that a recently installed software could be the culprit, especially if it involves media files by messing with codecs and drivers. About two weeks ago I had installed the VLC-player and I figured it might do no harm if I uninstalled it. Also, I did a disk check on the Q3 (which took 10 minutes and didn't find any errors) and when I tried it again this morning it took the PC only one minute to find the Q3 and gave me no i/o error!
I still don't know what had caused the error but it seemed to be a driver and codec problem (maybe the VLC player wanted access to the files and the computer blocked it for safety reasons, causing a hang up? I'm not an IT specialist but I've had similar things happen) but it seems to be solved now, more or less. One minute of waiting time without an i/o error might not be nice but it could be worse *lol*.