Is it possible the password was forgotten and is being entered incorrectly? I had exactly this issue with Gmail with an old gmail account I hadn't used for a long time, couldn't remember the password and it does this - it sends you in a loop. There are many many people complaining about this on the internet. There was no way I could get into that account, using all the verification it kept asking me for - I tried everything. You can't seem to get contact with anyone either. What happened in the end was - I found the original password written down somewhere, logged in and all was fine.
In a way it's a security thing if you don't enter the correct password, but the verification is ridiculous and doesn't work. If someone else HAS actually hacked in and changed the password, then you won't know the password obviously. But this verification thing has always been in issue with gmail.
I would think very carefully about whether the password is correct - was it changed and you forgot? Was one letter in upper case rather than lower. My gmail account was locked for a year! Until I found the original password!
