Blue screen - unmountable_boot_volume


I bought the My Passport Essential (320 GB).  Once the installation is completed, a blue screen appears and ask me to restart my PC.

So, I restart my system and I have always a blue screen “unmountable_boot_volume”.  I try all start mode (also the safe mode) and the blue screen is still there.  I use this laptop (with Windows XP) for working, so it’s very important that I can’t loss data.