Win98 domain logon problem.

We are a network of approx. 150 nodes. A couple of weeks ago we had a power shutdown of our site, since that time, probably a dozen Win98 boxes, after a shutdown and restart only get the two-tier Windows logon instead of the three-tier domain logon.To get around the problem of logging on to the domain, you must either enter your Windows password and say ‘OK’, or hit cancel, let the box finish it’s startup, then logoff, and you immediately receive the three-tier domain logon! We have tried editing the msdos.sys and looking in the registry for autologon values. The nic cards are configured to logon to the domain, we are at a loss for ideas here. Everything else works normally. Help please!