Exchange 5.5 trouble

[tk421]

We've been having a great deal of instability with an Exchange 5.5 server we have. It was purchased a year ago, and it is running Windows 2000 server. It has AD installed and is our primary DC.

Ever since it's been our mail server, it's been fairly unstable. Every few months we have to reboot it. Every few weeks OWA stops working, and we have to restart the IIS services. The last few weeks have been terrible. We have to reboot the server every week, and this week we've rebooted three times since sunday!

I've compiled the symptoms, and i'm hoping that someone can shed some light on them for me:

DCOM errors: In the event viewer since July 22, there are over 40,000 DCOM errors. Event ID 10010, Description:
The server {6EE7E990-8CBB-11CF-BF69-080009B4DB7F} did not register with DCOM within the required timeout.
These occurred every 30 seconds until 8/3 (Sunday). The Exchange services stopped responding shortly after.

LDAP: I never changed the LDAP port for Exchange, and i understand AD uses the same LDAP port. Would this cause this rampant instability?

Windows Network Server service: Often when i find the Exchange services have terminated, this service is stopped. I cannot start it, as it reports this error message:
Could not start the Windows Network Server service on Local Computer. The service did not return an error. This could be an internal Windows error or an internal service error. If the problem persists, contact your system administrator.

Currently, I am no longer receiving the DCOM errors. I just changed the Exchange LDAP port to 390. Exchange is up and working (for now), but the Windows Network Server service is still not starting.

Any ideas on where to begin troubleshooting?