I have had quite a time of my PC slowing down, files misbehaving, strange things happening and yet virus free and 'clean PC' being shown each time.
I backed everything up ------ then found a wonderful piece of advice that showed how to completely restore Windows without losing any work or settings, saving hours of hanging around and reinstalling. I set this system going --- it was like a dream, wonderful. I got to the bit where I was told to remove the CD ... yes, that was just as expected. THEN, the computer said it needed 'such and such' a file. The file was on the CD I had just been asked to remove. %Q£%$H*&%&^%Q%J?:@L ... the CD then decided to launch into a complete wipe clean off my hard disc and a complete re-installation of Windows! Well at least all my problems have been cleaned away. 

My next job will be to add certain files to a separate disc!!!!