The first thing you should do upon disovering that you can't get into your account is make sure you are on the right site. If it has been a while since you logged into Habbo you might not know that Habbo.Com now leads to the US Habbo rather than the UK Hotel.

Secondly check if you have typed the name correctly. Punctuation marks may have been mixed up. Also check if your caps lock is on as the passwords may be case sensitive. If it is a new account remember you may have typed the password you wanted wrong when you signed up.If this is the case then you shoul contact the Hotel Staff.
If it is an older or regularly used account, then you should create a new habbo temporarilly and log into the site. When you are logged in search for your original Habbo name on the < a href="shortened.htm">console. If it is still there and the wording you typed under the name is different then someone else has the account.

You should run Ad-Aware on your computer just to make sure you havn't been keylogged. And of course the hacking should be reported.