Well, well well...
Trying to install a BDC and you install a PDC instead. Tbui, you are on the wrong footing. I wonder how you demoted a newly installed, a fresh, PDC to a BDC, in absence of any existing BDC.
The new PDC you installed is born in a new domain, and it will connect to your existing PDC through trust relationship. Any BDC you install to the new domain will not talk to the old PDC directly.
As we told you earlier, the problem can be the network connection. The new BDC your are trying to install cannot connect to the PDC during installation. That's your problem. And you are the best person who can find the solution. Check the network cables, driver of NIC, admin password etc.
Any MS domain can have one and only one PDC. You can have as many BDC as you want. There's a lot I can say... but just do the whole thing again if you wish to have a BDC in your existing domain.
Mubashir