My son's PC (Dell Dimension 4700, Win XP SP 2) displays a blue screen of death with the message 'UNMOUNTABLE_BOOT_VOLUME'.  It will not boot to safe mode or any other options and always comes back to the bsod.  MS KB suggests thgat this is some sort of HD failure and suggests that Windows be reloaded.  When i tried to reload from CD using the onboard CD/DVD R/RW it wouldn't find the windows CD.  I went into the BIOS to see what the boot sequence was and it does not recognize the CD drive in the boot sequence.  I says the 'Onboard or USB CD-ROM   (not present)'.  When the PC was working, it would read and write CDs and DVDs so I don't understand why the BIOS doesn't recognize the drive.  Any help would be appreciated.

My next plan is to buy a USB CD-ROM and see if it is recognized.  The original problem (unmountable boot volume) may require that my son buy a hard drive but I'd like to try loading Win to the drive before throwing it out.  Thanks.