Quick Question if anyone can answer.
My employers have just moved premises which entails moving the server at the same time we have not renewed the contract for the old IT bloke(bit of a nutter).
Is it possible for him to lock the server by changing the password remotely?
Will there be a log of this?
How can we get back onto the server?

If the password is changed on the server then everyone who is connected to the server will disconnect. The only way to re-connect is if you enter the right password.

That's not the case actually. Even if the IT guy changes the Administrator password, you could still boot the server up and have it functioning normally in terms of users still working on the networked PCs around the office and still using network services such as Internet, printing, etc. However, the time will come when you'll want to log on to the server to check the backups, add a new user or .... well, pretty much anything to do with I.T. and, without knowing what the password is, you're basically stuffed. You would need some third-party password-cracking program, which we won't give ANY advice on here for obvious security reasons.

Best way to make sure that you can log in all the time is make sure that you don't have only one person who is an administrator or knows the password for the Administrator account. Once someone else knows how to log on as an administrator, they can disable the dial-in / remote access permissions for the I.T. guy (assuming that they know how to). That way, he won't be able to connect from outside the building .... unless he has installed a remote support tool such as LogMeIn.

I know that this doesn't tell you how to have a guaranteed fail-safe solution but I'm afraid that a disgruntled I.T. guy is one of the most dangerous people that you could have in your building (or outside your building!) and he will generally know more about network administration than anyone else in the organisation. Bit of a tough situation without a great answer really. My tip is to get an IT consultant in to make sure that EVERYTHING about the network is fully documented - this is expensive but it will be worth it if the I.T. guy can currently lock the network down and hold you to ransom.