I see an answer to your post at Dell support.
My father's laptop wont start up. It boots but stops on a black screen saying "DWTHY Compressed. Press ALT + CTRL + DEL to restart". We do that to see what happens but its the same story. My father says that he went into C and right clicked on something and hit compress to save some space. Afterwards everything was fine. He turned off the computer later and worked just as well. But today that message showed and wont let windows start. Anyone know whats going on.