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 M... compressed, and 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.

[Troy Clubb]

My friend compressed her hard drive and now it will not boot to windows and says it can not find bootmgr. How can I uncompress her drive so that it will be operational again