I noticed this problem a few weeks ago: when trying to move unneeded files off my laptop onto my external hard drive to free up some space, the computer made a "ping!" noise (the noise it makes when you are trying to drop something somewhere "illegal") and the files didn't move. This happened whether I cut or copied & pasted it, or clicked and dragged, or anything else I could think of (when I click and drag rather than copy/paste there is no noise though). I thought it was a temporary problem and didn't give it much attention until I realized that I can't move stuff around on my computer, either. On my desktop, if I pick up a document and try to drop it into a folder, nothing happens.
I'm at a total loss as I can't find anything about this problem on the internet, and my laptop is almost entirely out of space.