Manual restore registry to the state that was just after installing Windows

Windows 2000/2003/XP/Vista/7/8/10

If you have no backup files created before the problem then you can restore your system to the state that was just after installing Windows. Then you will probably need to re-install some programs again.

In this case you need either another copy of Windows installed or Recovery Console installed. Read install Recovery Console and how to use it topic.

There may be several variants to boot into another copy of Windows (at least Windows XP is required):
  • a second operating system installed on that machine;
  • or install a new OS into another folder (not C:\Windows originally) or another partition;
  • or connect hard drive to a machine with Windows installed;
  • or make a boot CD or flash drive with Windows or another OS with support of NTFS.
The better and easier choice is using a boot device. There are a lot of bootable images in the Internet especially designed for Windows recovery.
Boot into your parallel installed system or Recovery Console, open in your problem Windows folder and find the folder: 

"C:\WINDOWS\Repair" for Windows® 2000/2003/XP or
"C:\WINDOWS\System32\config\RegBack" for Windows® Vista/Seven.

This folder contains registry backup files created at the time of system installation ("C:\WINDOWS\Repair") or files created on previous successful system start ("C:\WINDOWS\System32\config\RegBack"). Folder "C:\WINDOWS\Repair" may also contain the "RegBack" subfolder with backup files created by the Backup utility.

If you boot into another Windows copy then you can use explorer to make file operations. Please select View > Details from the explorer window to see file creation dates. Find the most recent file with the name system from one of these two folders (Repair or RegBack) and copy it to the "system32\config" directory ("C:\WINDOWS\system32\config"). If this folder already contains system file then rename the previous file to system.bak before.

If you are under Recovery Console type these commands: 

cd c:\windows\system32\config
ren system system.bak
copy c:\windows\system32\config\regback\system c:\windows\system32\config\system
All of the mentioned above folders (Repair, RegBack, config) may contain other registry files: default, sam, security, software, system.

Try to restore first the system file and test loading the system. Only if this didn't help then try to restore other registry files one-by-one with testing between restoring.

Registry files
SYSTEM file is the "HKEY_LOCAL_MACHINE\System" registry hive
DEFAULT is the "HKEY_LOCAL_MACHINE\.Default" hive
SAM is the "HKEY_LOCAL_MACHINE\SAM" hive
SECURITY is the "HKEY_LOCAL_MACHINE\SECURITY" hive
Both last mentioned files contain system security records. Don't modify these files if you don't know what you're doing exactly.
SOFTWARE is the "HKEY_LOCAL_MACHINE\Software" hive
It contains registry keys for installed software. If you replace this file with one old then you probably will have to re-install the most of your programs.