CentOS 6.3:Cannot login as root despite the password being correct. Same password working correctly for days

Freckles asked:

Possible Duplicate:
Why is “chmod -R 777 /” destructive?

I have CentOS 6.3 minimal installed. No desktop or GUI. All the while, I was able to login as root. Today, I come to work and find the same password no longer works. I was the only one who knew the password and no one in the office touches this machine. I have verified it using CCTV.

When I enter the password it gives me the following error:

centos2 login: root
Password:
Login incorrect

I have tried SSH via Putty as well as WinSCP. I get Network Error: Connection refused.

So what could have gone wrong?

Please advise.

Please Note: root is the only user on this machine. I have not made any other user yet. Or maybe I did but I cannot remember since I have been using root for several days now.

UPDATE:
I tried to reset the password following the instructions on some other site. All went well, except I get the same error despite changing the password!

UPDATE:
This server is my test server and I try a lot of things on it. The last major thing I did was to select all the directories in WinSCP and give them 777 permissions. Could this have anything to do with the problem?