My son has a Dell Dimensions comp w/ Windows XP system
He was online & then all of a sudden a million pop ups came up & could not be stopped. So he turned off the computer & now Windows will no longer load but brings us to a page saying that Windows has shut down to save the computer from damage & gives the Unmountable_boot_volume message.

I have tried to restart & work in safe mode but no matter what choice I make (Safe mode, command prompt, last working, etc...) the comp acts as if its loading & then goes back to that ominous blue screen with the Unmountable_boot_volume error.

We tried to restart with his XP CD & every CD that came with his comp. Doesn't work. I made a floppy MS Dos boot disk from my comp & tried restarting with that - still same screen comes up Unmountable_boot_volume

Any suggestions before my son throws it out the window................

I don't know what discs you have with your machine, but first you need to change the boot order - early on in POST hit F10, or maybe Del, and change the order so that CD boot is first...[if HD boot is first your sys will not search any further]. Now you need Recovery Console; when in that run:
chkdsk /p
No go still? Then run:
bootcfg /rebuild
in the console. A search will be made for any OS's on your machine, when they are found you will be queried about adding them to the boot.ini file.

It's possible you have an unbootable disk in a removable drive. If so removing that disk will allow the compoter to boot.

A virus may have replaced the boot sector.

Or shutting the computer down wrong
damaged the boot sector.

You need your original windows disks to fix this.