2140 error for Exchange Event Service

1. 2140 error - can't start exchange event service

Help appreciated.  Here's what happened:
Server I'm working on has Exchange 5.5 set up on a PDC
running NT4. (not my idea!) and "administrator" as login
service user for all Exchnge services.
Admin password was changed.  Exchange won't start at all,
giving "invalid logon" messages.  I changed pw back to old
one.  All services started except event service.  I tried
different user, different password for admin, old password
for admin - noluck. Tech refs say change the user assigned
to run the service - no luck.
Any ideas?  This is, of course, the company's "main,
lifeblood, etc" system.
Thanks

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