I have created a separate lab to test the FIM 2010 R2 Self Password Reset Portal. It has installed successfully but while clicking on 'Password Registration Portal' it is showing page cannot be displayed

I would start with the IIS Bindings -- to which IPs and names is the Password Registration Portal bound?

Try to access the site directly. It could simply be that the link is incorrect. The link is stored on the FIM Portal server in HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Forefront Identity Manager\2010\Portal  and look at the value of RegistrationPortalUrl