Dell were telling lies
http://www.computerforum.com/184833-windows-stop-error-guide.html#post1544398
Code: 0X000000ED
Message: UNMOUNTABLE BOOT VOLUME
Cause: There are 2 possible causes for the problem, both of which are related to the hard drive.
The first, some IDE hard drives will write data to the cache out of order to increase the speed at which they work. This can cause integral parts of a program or the operating system itself to become damaged if the system loses power, or there is an unexpected shutdown.
The second is if the SATA controller is toggled from ATA to AHCI, or vice versa, in the BIOS. ATA and AHCI need different drivers, so swapping from one to the other will cause problems, as the drivers are not installed
Fix: You will be able to tell which problem you have, by the type of hard drive that you have
If you have the problem with the IDE drive, you must first run the windows repair tool. To run this, put your Windows installation disc into the disc drive and boot from it. There will be an option to repair/fix a windows installation. Do so, then try rebooting into windows.
You should now be able to boot into Windows. Disable write caching. To do so:
Right-click My Computer, then click properties
Click the Hardware Tab
Click Device Manager
Click the + sign next to Disk Drives
Right click the drive which has your operating system installed on it, and click properties
Click Disk Properties tab
Uncheck the Write Cache Enabled box
If you are running Windows Vista/7, Device Manager is in control panel as its own area, you don't need to go to system
If it fails to fix it, and you can not boot into Windows at all, you will have to format your hard drive and reinstall Windows, as it is too badly damaged.
If you are experiencing the problem with a SATA Hard drive:
Go into the BIOS, and change the SATA controller configuration back to whichever it was by default. Boot using your windows installation disc, and run the repair tool and let it fix any errors that may have been created, then try to boot into Windows.
If that does not work, run the hard drive utility for your hard drive. Each manufacturer has their own, which should be used for their drives only, and no other utility for a different manufacturer's drive should be used. Go to their website to find it. Remember that each is bootable, so you will either need to burn the file to a disc in a bootable file format, to a floppy disc, or to a USB device, should your motherboard BIOS support booting from a USB device. If it fails, your hard drive is dead, and you will have to get a new one. First contact your manufacturer if the drive is still under warranty, as they will replace it for you free of charge should it be faulty, and is still under warranty.
If the test passes, but you can not boot into Windows, you will need to format your hard drive and reinstall Windows