Well it can be as simple as that:
The pooters are not perfect and from time to time made small mistakes reading and rewritting information, the only thing you need is that that small mistake is in the wrong place and then the pooter cannot find the file or does not recognize it.
If the computer does not recognize the file, numbers are you need to open it somehow and then close it, normally this is done right and the problem is sorted, if on the other hand you cannot open it, numbers are you'll have to replace it (the file, not the pooter!).
If the computer does not find the file, either it is not there (and you have to replace) or simply it as lost the adress, on defragging, all files in the computer are read and assigned new HD addresses and then the pooter can find them again. :isadizzy:
A bit long, but I hope it helps understanding the mental dwarfs (pooters
) that are our partners in crime.
Saludos