You need to boot to recovery console to fix this.
Then type
md tmp
copy c:\windows\system32\config\system c:\windows\tmp\system.bak
copy c:\windows\system32\config\software c:\windows\tmp\software.bak
copy c:\windows\system32\config\sam c:\windows\tmp\sam.bak
copy c:\windows\system32\config\sercurity c:\windows\tmp\security.bak
copy c:\windows\system32\config\default c:\windows\tmp\default.bak
delete c:\windows\system32\config\system
delete c:\windows\system32\config\software
delete c:\windows\system32\config\sam
delete c:\windows\system32\config\security
delete c:\windows\system32\config\default
copy c:\windows\repair\system c:\windows\system32\config\system
copy c:\windows\repair\software c:\windows\system32\config\software
copy c:\windows\repair\sam c:\windows\system32\config\sam
copy c:\windows\repair\security c:\windows\system32\config\security
copy c:\windows\repair\default c:\windows\system32\config\default
Make sure you hit enter after each line.
This should fix your problem.
If it doesn't try typing fixmbr at the recovery console.
If you can't get into a recovery console boot into dos using a 98 boot disc
then type the same.
: )
