I cancelled the factory recovery process on my Toshiba Laptop L645.
It corrupted the hard drive somehow, and I can't open a file on the hard drive – so in the end I had to reformat my hard drive.
What caused this?
Starting factory recovery restores a system image onto the hard drive, effectively the same thing as formatting the drive in the first place. Since you cancelled it, the image was not completely copied and the partition was invalid or missing files.
Essentially, once you've started factory recovery there is no way back. You might be able to find some of your missing files if you use a data recovery program, but don't count on it.
Remember - files you don't have backed up are files you didn't really want that much in the first place.