Copy the error message you get with the blue screen down word for word and post it

The error message was pretty long as you can imagine, so this isn't verbatim-but very close.

'If this is the first time you have tried to restart and you get this message, restart again.
If this message comes up again:
check new hardware or software to see if properly installed. If this is a new installation, (it isnt), ask the hardware or software mfgr for windows updates it may need.
If it continues, disable or remove newly installed hardware/software.
Disable BIOS memory options such as caching or shadowing.

If you need safe mode to remove or disable, restart and press F8 to select advanced options and select safe mode.'

This stop message was at the bottom of the error..
STOP 0x000000ED UNMOUNTABLE_BOOT_VOLUME" Error Message

I googled the 'stop' message, but am pretty nervous about what they say I need to do.
I left the link here.

btw-This defrag was being done right after a cold boot and a restore point was made just before that.

Here is a link that might be useful: MS stop error

Have you tried to boot into safe-mode or selecting last known good configuration that worked.
I guess with an unmountable boot volume, it's not going to boot at all.
Using the Recovery Console is easy, you'll need the xp cd.
Boot with the cd, press r for Recovery Console.
Then run chkdsk /r or fixboot from the command.

Looks like microsoft, for that link, may want you to consider that possibly you have the wrong hard drive cable. One would think if the bios is accessable there is a possibility that you could change the hdd mode to something a bit slower than UDMA.

There are more articles at microsoft that point in other directions too. Popular is to turn off ; hdd cache, and any read ahead or write behind options ,,, again if it is available in the bios and not automatic.

I'd probably open the case and check the hdd cable to make sure its plugged in securely on both ends and not all intertangled with other cables.

Here is a link that might be useful: http://support.microsoft.com/kb/297185?STOP 0x000000ED UNMOUNTABLE_BOOT_VOLUME

Dell didn't supply the CD's with this unit.
Anyway, those next steps kinda scare me. According to the info at MS site, I need to know if I have dual boot or multiple boot, and I dont know what that means.

dual boot means that you have more than one operating system installed and can choose which to boot to. I had xp and linux for a while, but finally gave up on linux.
Dell doesn't supply the windows cd but you are supposed to make one (called the dell os restore cd) using a utility that comes on the computer. It must be easy to overlook that instruction in the material that comes with the computer because several people have posted with that problem. I doubt that you can use the utility to make the cd if you can't boot up, so if it comes to that you may have to contact dell support. Someone may know if it will work to borrow a windows cd and use the file check.

Well, I have a conclusion.

I called Dell and my hard drive is gone! So glad I back up regularly.

I'm taking computer to a tech guy that my sister recommended.

Thanks everyone for trying to help.

Judy if you are taking the computer to a tech guy are we to assume your warranty has expired? Your tech guy will install a new hard drive but you may well (will) have to buy a copy of XP.

Good news that you back up regularlty, it would be great if more people did that with some kind of regularity.

The case should have the sticker and the product key for the oem xp home.

owbist, randy_ca:

Yes, the warranty is expired.

The Dell tech suggested I take it to a tech and see if can save any more data from it, before he removes the hard drive.
This same, wonderful Dell tech, is sending me the Win XP CD, and offered to help me install it when it came, but I may give it to the tech. I'll see how much he charges to put it on, and am thinking it may be worth the money to me.

Thanks for giving me your time.

Judy

update:

I received the 'Operating System CD' from Dell, as promised.

Get this: they also sent me 'software for re-installation cd's' for the bundled software, utilities, drivers and more-7 cd's in all.
Of course, they also ask that I send back to them, the defective part (HD) or they will charge me for the software.
Understandable, I guess. They need to know I'm not scamming them.

I don't think a lot of people would agree but I think it was good of Dell to do that.

update:

I received the 'Operating System CD' from Dell, as promised.

Get this: they also sent me 'software for re-installation cd's' for the bundled software, utilities, drivers and more-7 cd's in all.
Of course, they also ask that I send back to them, the defective part (HD) or they will charge me for the software.
Understandable, I guess. They need to know I'm not scamming them.

I don't think a lot of people would agree but I think it was good of Dell to do that.

I don't get it. Are they giving you a new HD for free? Why would they want it back otherwise?

I imagine they want the old drive because the operating system is stored on a partitionon it. Asking for it back ensures a person only has the new one, not both.