I haven't found any solution to the following issue, so I'm posting the help in this forum.

Issue : A user required re-installation of SolidWorks EPDM 2012 SP3. While performing "View Setup", after selecting the Production Server, the Production Vault cannot be added as it shows inactive (grey-out) as per the following screen :

Resolution : Cancel this vault setup.Go to Start > Run > regedit. Look-up to the following path and remove Production Vault (folder icon) under Databases.

(HKEY_LOCAL_MACHINE\SOFTWARE\SolidWorks\Applications\PDMWorks Enterprise\Databases)

Restart system and carry on with Solidworks PDM > View Setup; the Production Vault will show up in black(with check-box).

N.B.-  You can put a 'Like' if this helps !!