How to fix Blank Device manager

RESOLUTION:
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CREATE A RESTORE POINT BEFORE ANY OF THESE STEPS
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STEP 1:
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Check if Plug and Play service is started.Check the settings of the same in the
registry

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\PlugPlay

ImagePath = %SystemRoot%\system32\services.exe
ObjectName = LocalSystem
PlugPlayServiceType = 3
Start = 2
Type = 20

STEP 2:
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Advanced cleanboot (316434) and Hardware cleanboot (SOX051008700004)

STEP 3:
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System restore (306084)
If we know when the issue started, read the system restore point information for
that day prior to trying the restore

STEP 4:
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Look for the update KB905749 and try uninstalling it. Be sure to shut the system
down and wait 10 seconds before restarting.

STEP 5:
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Go to safe mode - check for bangs in hidden devices in System devices - Uninstall
PnP BIOS Extension and any other device having a bang

STEP 6:
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- Follow SOX041029700032
check the permissions on
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Enum
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Enum\Root
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Enum\Root\LEGACY_RASAUTO
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Enum\Root\LEGACY_RASAUTO\0000
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Enum\Root\LEGACY_RASAUTO\0000\Control
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Enum\Root\LEGACY_RASMAN
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Enum\Root\LEGACY_RASMAN\0000
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Enum\Root\LEGACY_RASMAN\0000\Control
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Enum\Root\LEGACY_TAPISRV
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Enum\Root\LEGACY_TAPISRV\0000
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Enum\Root\LEGACY_TAPISRV\0000\Control

If Administrators is listed, then remove Administrators. The default permissions
for these keys are:

System : Full Control : This key and subkeys
Everyone : Read Only : This key and subkeys

Change the permissions so that they apply to "This key and subkeys" and not just
"This key only".

STEP 7:
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We could try to register the following files
regsvr32 devmgr.dll
regsvr32 dmocx.dll
If the files are missing, extract a copy from Windows XP CD-ROM or the
ServicePackFiles folder

STEP 8:
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Copy the following on a notepad.Save it as dev.reg.Double click on the same.Restart
the computer.