To re-install exchange on a formatted BD

My client network consist of Win2k PDC and BDC.
PDC had SQL and JAVA whereas,BDC had MS Exchange,
Somehow BDC was accidently formatted.
Now when we try to load MS Exchange after installing and configuring BDC it is not allowing us to proceed and gives a PDC error.
Is there any change to be done on PDC so as to install Exchange on BDC without getting the PDC error?
help appreciated.