Boot the dvd to system recovery options:
( Boot dvd - windows loads files - select language and keyboard -
when you get the Install Now screen , DO NOT CLICK "Install Now" ,
instead click "Repair my Computer" at the bottom left of that window ).
It will probably attempt an automatic repair - worth running that a couple of times to see if it helps.
If not, highlight the o/s to repair, click Next
Open the command prompt
Type the following - press enter after each command ( after each line):
cd windows\system32\config
ren default default.old
ren sam sam.old
ren security security.old
ren software software.old
ren system system.old
cd regback
copy default c:\windows\system32\config
copy sam c:\windows\system32\config
copy security c:\windows\system32\config
copy software c:\windows\system32\config
copy system c:\windows\system32\config
Close cmd prompt, restart - boot from HD. With any luck you will boot up fine.