When the hdd is going down
When you make a fresh Windows 7 install in a tired machine and the process of expanding files takes a looong don’t go away, before change optical drives, or select another setup solutions like flash drives etc. think that maybe your hdd needs urgently change.
The same if in Windows XP setup presented missing files (and prompts you to press F3 to continue). The hdd is the first suspect.
Think about it before you waste your day in experimental installations