Unmountable Boot Volume

If your computer boots up with an "Unmountable Boot Volume" on a black screen and won't go past that, then there's a problem with the hard drives partition table. There are a few ways to solve this:

Recommended Tools:
-Bootable DFT
-Windows Recovery Disc
-Windows Bootable Enviroment

Steps:
1) First test the hard drive status using Bootable DFT
2) Even if the drive fails just note the error code, usually 0X70 or 0X72 are file system errors while 0X74 means a SMART failure (which would mean the drive is dead)
3) Boot off the Windows CD
4) Hit "R" to enter the Recovery Console
5) Select the Operating System you are repairing
6) Once you reach the command prompt type:

"chkdsk /r"

7) Chkdsk will run through a five stage process, once it completes restart the computer
8) Upon startup run the Bootable DFT program again
9) If there are no errors returned the problem is fixed, reboot and see if you can access Windows. If you get another error it would be best to consult your manufacturer and replace the hard drive.