RPClocator service error

I have an NT 4 server which is a PDC running Exchange 5.5. Recently the server seemed to hit a brick wall and all services stopped responding. If you try and access the services from Control Panel or at Command level you just receive a stop error “the RPClocator service is unavailable.

The funny thing is when you boot the server you don’t get any service failures.

The server does eveything extremely slowly, i.e logging on, opening explorer etc.

Thanks in advance
Evan