Exchange 5.5 not receiving mails

We are still using an exchange 5.5 on Windows NT just to keep an old email address alive so that we still could get the mails from our major client. We are still in the process of changing our contact email in their system which require tons of paper works, etc.

What happened was there was a power failure for almost an hour during the night and the old UPS was not able to maintain the required time before it sets the server to automatically shutdown (it's an old ups btw), therefore the server shutdown without going through the normal process.

The next day when I came in at the office I started the servers and it worked fine. Exchange worked normally except that it does not receive any mails anymore. Our mails pass through our ISP's relay server, and they informed me our mails are in queue in their servers and cannot get through to our exchange server.

This is the message when they test our smtp: "the SMTP port is open, but it is not responding with a hello response to any SMTP connection request." and "ERROR: Error connecting to host mail.domain.com:25, Operation now in progress.."

Nothing has been changed in the server as well as the exchange. Anyone who might be able to help is appreciated. Thanks in advance.