Domain Reconfiguration Error

Recently my network underwent a life change!!! In attempting to label and test cables in a closet housing an elevator motor (really!!!) Temps range close to 100 degrees in there! Everything came crashing down…Also the AS/400 was replaced and we installed a server rack/table to house the 400 and my servers. At any rate my PDC & BDC now “distrust” each other because of a DOMAIN RECONFIGURATION and the SIDs are lost.
I must Reestablish the trust? Can somebody help me …I’ve tried talking tothe PDC & BDC but they just won’t listen!
Thanks,,
Digitally Challenged Administrator