@
BunnyGal 
You could also try running in Windows Safe Mode
Simple way to Safe Boot: Control Panel->Administrative Tools->System Configuration (or type msconfig in start menu search). Go into Boot tab, check Safe Boot and select Minimal. Restart Windows. To get back to normal boot, uncheck Safe Boot whilst you're in Safe Mode.
If that yields nothing useful, then it might be worth doing a System File Check, here's how ==>>
How To Use SFC Scannow to Repair Windows System Files
Which edition of calibre are you using - 32bit, 64bit or portable?
BR