[cybmole]

quick note on clean install- the windows uninstall does not remove calibre's app data folder(s) so if the problem is with something in those...

something like Revo uninstaller will do additional searches for related files / folders or you can manually locate and remove what is in app data.

the app data stuff is , for me, the most likely culprit given your reported facts.

it seems that every program on your PC is working just fine,except for calibre, so i't s unlikely to be some other program causing this issue. I would, in your shoes though, do 2 x through malware checks, e.g. run both trend micro house calls and malwarebytes scans, just to be sure that the PC is clean.

and run microsoft disc cleanup ( chkdsk ) on its most thorough run-at-startup settings, in case you have orphan file fragments or bad disc sectors that are somehow causing this- my computer: right click on C:\ drive -> properties -> tools- error checking...

the suggestion with Ccleaner is that you go to tools -> startup -> inspect all 4 tabs for any strange program or task running at start up (& google anything dubious)

i'd also try having calibre place its library on a separate hard drive ( or on a USB stick if you don't have a 2nd drive) & see if you get the same behavior. if so , then it is not an issue with your specific hard drive file allocation tables.

it's all about patiently running overlapping tests so that you can eliminate suspects....