You may follow this :
1) Locate the following key in the registry:
HKEY_LOCAL_MACHINE\Software\Classes\Installer\Products\ompressed GUID> where
is the 32-character unique GUID for your product if known
2) Export this key to a safe place and then delete the key from the registry. If the unique GUID for your product is not known, the whole key
HKEY_LOCAL_MACHINE\Software\Classes\Installer\Products
can be exported and then
deleted.
3) Attempt the installation of the product
4) Once the product is installed, the key
HKEY_LOCAL_MACHINE\Software\Classes\Installer\Products or
HKEY_LOCAL_MACHINE\Software\Classes\Installer\Products\ompressed GUID> can be
imported back to the registry.
--Apparently this problem arose because the installer, based on the presence of
this key, believed that SQL Server 2005 already existed and so it skips installation od other components like db services,NS,RS,AS etc.
The other workaround is :
1) Go to Add/Remove Programs .
2) Remove MSXML 6.0 Parser (or any other version of MSXML parser which exists)
3) Start installation of SQL again.
Some times you may have difficulty removing MSXML parser, you may use Windows clean-up utility to remove MSXML 6.0 Parser .
HTH
