As Warriorstrike had said, the site is undergoing maintenance.
Once it has finished, the registration will open.
When it does, try to stay up quite late. Then the registration is likely to open. I discovered open registration from getting back from the store, and got an account. So registration opens at random times. Refreshing the page every few minutes will get you nowhere. Red had said in a post:
How does the registration actually work?
How the registration is set up currently is to randomize times throughout the week the site will open up the registration. These open registration times can vary greatly, it can open in early mornings, late mornings, mid day, early afternoons, etc. Once the registration actually does open it will show a new option in the yellow box next to the banner to register an account, but that's of course only when it is open.
When/how often does it open?
In this case, random is random so no one can tell or predict when it will be open, if registration were to be open at a certain time one day it doesn't have to open that time the next day. What can be said though is that it tends to be open several times every week, and every time it does open it opens for 2 hour stretches usually opening(or closing) when an hour changes, this means reloading the page every five minutes will not be the best way to get an account and will not increase your chances directly, instead maybe consider checking in every two hours for best effect. Just keep checking in and you will find an open registration time eventually!
Hopefully it all works out for ya!
If you already use your gmail account for a FH account, you will not be able to use it for another one. You will have to use a different gmail account altogether.