Bit of a system scare, but nice to figure it out

I was moving files around when suddenly the system wasn't doing things I expect it to do. Then I figured out whatever it is, it was a system thing and not a hardware problem.

Basically, I moved some PDF files around and of course the Acrobat Reader part of the system kicked in so it could offer me a thumbnail in My Computer. However, if you deal with many PDFs very quickly, moving them from one directory (aka folder) to another, the Acrobat Reader system thingy can get confused. The result: You get more than one process named AcroReader trying to access files you just moved, and then one other file that you moved also ends up unable to be accessed. My Computer stops offering preview thumbnails for images. You load up My Computer, and it hangs, trying to find your drives. It seems you're having problems with your hard drive! Scary!!

Essentially, a system process was still trying to access a file on C drive. When a program continues to access a file, you get problems. When it's trying to access a file you moved, it's worse because it's trying to work with the file where it used to be and now it isn't there.

The solution was to end the AcroReader process (I had 2 going at the same time when this happened), and when they disappear, your drive is free again.