Hendrick Router Stuck in E-Stop

We have a 1990s era Hendricks router that is exhibiting communication issues; initially the computer was showing 1004 Host Error - Host Cannot Be Ready. On a couple occasions, we have also seen Error 1007 - communication with PLC. We did some board swapping and connector reseating. We put in a new PCI Serial I/O Board and a new PCI Control Board - Nova MC8041P. Tried those boards in different PCI slots; this is a Windows 2000 (NT) computer. Still stuck. Any suggestions on what to try next? Thanks