I've had no problems with mIRC or connecting to servers until recently when I moved to a new building. We have the same operator for our line though. Another new thing is our firewall (Norton Internet Security 2003), but I've created a rule for it so that mIRC should be able to connect anytime on all ports.
Somehow, this isn't enough and I'm getting the "Unable to connect(connection timed out)" message anytime I try to connect to any server.

Can anyone please help me?

Check the website for the network involved to be sure you are trying to connect to a working/linked server. (If its DALnet, that can change from moment to moment right now)You could try increasing your time out in seconds line in file/options/connect/options (click on the retry button). Wouldnt hurt to double check to be sure you arent blocking the server ports or mIRC.

Not sure what you mean by "same operator" but if you are at a school, its poss the sysadmin made some changes.