how can I uncompress windows 7 (the whole hard drive)?

[Anabelaoliveira]

I was trying to save space on my hard drive and compressed everything by mistake. Now when I try to turn the computer on it appears a message saying the MGAQW is compressed, and press Ctrl+Alt+Del to restart, I do this but it does not let me boot the pc at all. How can I fix this and boot the computer again without loosing any data that I had before. Please help me.
Thank you.

[RuralGuy]

Do you have another computer you could install this hard disk into so you could decompress it? How about booting from the CD/DVD and then decompress?