Looks like you need to take a look at
http://support.microsoft.com/default...b;en-us;555302
Basically provided you haven't switched cables or been monkeying with your BIOS you should be able to sort this by booting from your install CD and selecting the option to Repair (r) to take you to the command line (recover console - it's not as scary as the above posts suggest - I promise!). From there you need to type
chkdsk /r
and press enter. Allow that to run (this may take some time dependent on your drive size) but should be able to sort your issue. Once this is complete type
exit
then enter and reboot your machine.
If that doesn't work you could try fixboot instead of chkdsk /r by using the same procedure. Let us know how you get on.