Windows XP client failing on NT4 network

Recently set up an XP client on Win NT4 SP6 server based network. After a short time the XP machine dropped off the network and now cannot log back on. Client event log shows event 3210 and 5719(?), both concerned with machine account. Server event log says no trust relationship exists with that client. This happens even if client is renamed and rejoined to the network. Any ideas??